EXPERT WITNESS: A COMPUTER SCIENCE EMPHASIS Allen Coleman David A. Dampier Department of Computer Science and Engineering Mississippi State University dampier@cse.msstate.edu Abstract Expert witness testimony is an essential factor in computer forensics work. Any computer scientist who engages in computer forensics work may eventually be called upon to testify in a court of law and to render an opinion about computer evidence. This paper outlines issues relevant to computer scientists who may be called upon to perform as an expert witness. Laws, as well as opinions are presented. 1. Introduction In any court case, two key aspects of both the defense and prosecution are witness testimony and evidence. An expert witness can provide a critical link between the two. Material witnesses are only allowed to communicate facts they know in direct examination. Expert witnesses provide a slightly different type of testimony that can make a dramatic impact on a trial. This paper has an emphasis on the possible role of a computer scientist as an expert witness. 1.1. Expert witness Experts are individuals who have extensive knowledge of a specific subject. An expert witness is an individual who is called upon in a court case to provide an opinion about evidence to in the realm of expertise. A computer scientist may be called upon to provide expert testimony in a variety of situations. Today, there are numerous court cases that involve computers or computer media as evidence. In any case were a computer is involved, a computer scientist may be used to analyze or interpret evidence. Computer scientists may also be used throughout an investigation to search a computer for evidence and eventually testify about his or her findings in court. Expert witnesses have different responsibilities than material witnesses. The primary difference is that they may provide their opinion, while material witnesses may only discuss facts [13]. Before an expert s opinion is admissible in court, he or she must meet three criteria. The must be qualified, their testimony must be relevant, and it must be helpful to the understanding of the case [15]. Experts are usually rewarded for providing their opinion to the court. They are almost always paid for their services, because the testimony they provide can be essential in determining the outcome of a trial, either by the defense, the prosecution, or the court itself. Whether they are paid by the defense or by the prosecution, their allegiance is still to the court and the truth. The evidence may not always be clear and an expert s opinion may provide the judge or jury a better understanding, which will enable them to better judge the case. 1.2. Legal system The American legal system can appear very complicated to anyone not familiar with it. For an expert witness, there are very few aspects of the system that must be understood before getting involved. An expert witness has a specific and important part in a court case. A case may hinge on the testimony of an expert. In some cases, if the testimony of the expert is not allowed, then the party will have no case [9]. The judge will make the final decision about whether the expert s testimony will be allowed in the case [7]. The expert is not required to provide opinions only favorable to the party that retains them. The ultimate goal of an expert witness is to provide an expert opinion on any matter for which qualified that is not clearly understood by the judge or jury. The expert must be familiar with the case and ready to answer any question from either party that pertains to the subject of which he or she is an expert. If the expert witness gives an honest and informed testimony of his opinions, then his or her responsibility ends when the trial ends. However, if the expert is negligent in preparing his or her opinion, then he or she can be held responsible for the negligence [10].
1.3. Terminology There can be an expert witness for any subject that is not considered common knowledge. The title given to the expert witness can be important. A computer scientist may be used to provide a variety of information and an appropriate title should be used. If the expert is providing information about a software product, the expert may be called a software analysis expert. However, if the expert is testifying about an investigation performed on a computer, they may be titled a computer forensics expert. The title describes the information that will be provided by the individual and also provides a basis for the opposing attorney to test the witness s credibility. The expert witness is responsible for any information that falls into the category that the title indicates and only that information [6]. The terminology should be chosen carefully when an expert witness is used. If the title is too broad, it may be easier for the opposing party s attorney to discredit the expert witness and therefore his or her testimony. 2. Who can be an expert witness? An expert witness can be anyone who has expertise in a subject that is not considered to be common knowledge. Expertise can be obtained by education, experience, skill, or training [5]. Once identified as an expert, the court must approve them before they can testify [6]. This is the simple requirement for an expert witness. However, it takes more to be an effective expert witness. To be effective, the expert must be able to defend his or her knowledge and opinions. It is not a requirement to have extensive academic qualifications, but it can help create a positive image for the judge or jury. Experience in the field in which he or she claims to be an expert is essential. In some cases, both parties will retain expert witnesses. If their opinions differ, it can be very important to have experience and academic qualifications in order to appear more credible. Ultimately, he or she must be competent enough to stand up to crossexamination and remain credible [8]. In 2002, there were more than 16 million cases in the United States and most used expert witnesses, therefore it is important to be extremely credible [4]. 3. The Law The Federal Rules of Evidence [5] provide a basis for the presentation of evidence during a trial in the United States. Every state may adopt variations, but the Federal Rules are used as a guide. These rules govern all types of evidence that can be presented during a trial, including that of an expert witness. Specifically, Rules 701 through 706 deal with the use of expert witnesses. The following sections provide the text of each specific rule and a brief explanation. 3.1. Rule 701 Rule 701, Opinion Testimony by Lay Witnesses [5], states: If the witness is not testifying as an expert, the witness testimony in the form of opinions or inferences is limited to those opinions or inferences which are (a) rationally based on the perception of the witness, and (b) helpful to a clear understanding of the witness testimony or the determination of a fact in issue, and (c) not based on scientific, technical, or other specialized knowledge within the scope of Rule 702. This rule describes the specific circumstances when a non-expert witness can discuss his or her opinions. There are three specific instances. The first instance is when an eyewitness gives their opinion on the events they witnessed. Secondly, opinion may be used to clarify a fact that a non-expert witness is trying to communicate. Lastly, opinions can be expressed when they are not based on specialized knowledge that would require the use of an expert. 3.2. Rule 702 Rule 702, Testimony by Experts [5], states: If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise, if (1) the testimony is based upon sufficient facts or data, (2) the testimony is the product of reliable principles and methods, and (3) the witness
has applied the principles and methods reliably to the facts of the case. This rule provides a general description of what an expert witness is and their purpose in the trial. The witness must first be acknowledged as an expert in the field in question. Expertise can be determined by knowledge, skill, experience, training, or education [5]. If the witness is determined to be an expert, they may then discuss their opinions of the evidence using proven methods from the field in which they are determined to be an expert. 3.3. Rule 703 Rule 703, Bases of Opinion Testimony by Experts [5], states: The facts or data in the particular case upon which an expert bases an opinion or inference may be those perceived by or made known to the expert at or before the hearing. If of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject, the facts or data need not be admissible in evidence in order for the opinion or inference to be admitted. Facts or data that are otherwise inadmissible shall not be disclosed to the jury by the proponent of the opinion or inference unless the court determines that their probative value in assisting the jury to evaluate the expert s opinion substantially outweighs their prejudicial effect. This rule describes the types of information an expert can use as the basis for his or her opinion. There are three instances mentioned in this rule. First, an expert can use any information that is made known in the case either before or during the trial. Secondly, any information that is deemed credible in the expert s field of expertise may be used, whether the information is admissible in court or not. Lastly, any information inadmissible in the trial should not be introduced to the jury, unless it will help them understand the opinion of the expert witness. 3.4. Rule 704 Rule 704, Opinion on Ultimate Issue [5], states: (a) Except as provided in subdivision (b), testimony in the form of an opinion or inference otherwise admissible is not objectionable because it embraces an ultimate issue to be decided by the trier of fact. (b) No expert witness testifying with respect to the mental state or condition of a defendant in a criminal case may state an opinion or inference as to whether the defendant did or did not have the mental state or condition constituting an element of the crime charged or of a defense thereto. Such ultimate issues are matters for the trier of fact alone. This rule states that an expert witness s opinion cannot be objected to during a trial. This implies that the only way to keep an expert opinion from swaying a jury is to present an opposing opinion, most likely from another expert. This rule also states the limitation of an expert witness s ability to testify about a defendant s mental state. 3.5. Rule 705 Rule 705, Disclosure of Facts or Data Underlying Expert Opinion [5], states: The expert may testify in terms of opinion or inference and give reasons therefore without first testifying to the underlying facts or data, unless the court requires otherwise. The expert may in any event be required to disclose the underlying facts or data on cross-examination. This rule describes the expert witness s responsibility to disclose the information used to generate his or her opinion. The rule states that an expert may testify to his or her opinion without disclosing the information used to formulate the opinion. However, if asked for the information, the expert must be able to provide it. 3.6. Rule 706 Rule 706, Court Appointed Experts [5], states: (a) Appointment. The court may on its own motion or on the motion of any party enter an order to show cause why expert witnesses should not be appointed, and may request the parties to submit nominations. The court may appoint any expert witnesses agreed upon by the parties, and may appoint expert witnesses of its own selection. An expert witness shall not be appointed by the court
unless the witness consents to act. A witness so appointed shall be informed of the witness duties by the court in writing, a copy of which shall be filed with the clerk, or at a conference in which the parties shall have opportunity to participate. A witness so appointed shall advise the parties of the witness findings, if any; the witness deposition may be taken by any party; and the witness may be called to testify by the court or any party. The witness shall be subject to cross-examination by each party, including a party calling the witness. (b) Compensation. Expert witnesses so appointed are entitled to reasonable compensation in whatever sum the court may allow. The compensation thus fixed is payable from funds which may be provided by law in criminal cases and civil actions and proceedings involving just compensation under the Fifth Amendment. In other civil actions and proceedings the compensation shall be paid by the parties in such proportion and at such time as the court directs, and thereafter charged in like manner as other costs. (c) Disclosure of appointment. In the exercise of its discretion, the court may authorize disclosure to the jury of the fact that the court appointed the expert witness. (d) Parties experts of own selection. Nothing in this rule limits the parties in calling expert witnesses of their own selection. This rule describes the process by which an expert witness is appointed by the court. This does not apply to expert witnesses retained by a specific party. The court may appoint its own expert witness or allow each party to submit nominations for an expert witness to be used if agreed upon. The expert witness appointed must agree to participate in the trial. The appointed witness will be informed of his or her duties beforehand and must submit his or her findings to each party. Either of the parties may choose to call the expert witness during trial and both parties can cross-examine the witness. The court will determine the payment of the expert witness. The court can make the decision to disclose the fact that the court appointed the expert. This rule also states that either of the parties can call their own expert witness during the trial. 4. Before Trial There are a few things an expert witness must do before the trial begins. The expert must first decide whether or not to participate in the case. An expert should consider the client s character and fully understand the case before agreeing to provide his or her services [3]. Once an expert agrees to participate in the case, he or she can begin performing the duties required of an expert witness. In the case of a computer scientist, there are two phases of the trial in which he or she could be involved. First is the investigation. If the computer scientist is involved in the investigation, he or she must use accepted computer forensics methodologies to gather and analyze the evidence. In addition to the investigation, a computer scientist may also be asked to testify during the trial. If so, he or she must review the evidence in order to form an opinion that will be put forth in trial. The following sections discuss the possible duties of a computer expert witness before a trial. 4.1. Investigation A computer scientist may be involved in almost all investigations that involve computers. This computer scientist will most likely be a computer forensics specialist and will likely be asked to testify during the trial as an expert witness. Therefore, the investigation becomes an important part of an expert witness s job [11]. There are many resources available for explanations of computer forensics methodologies and it is not necessary to discuss them here. However, there are a few important points to remember about conducting an investigation. Almost all forensics methodologies are based on the needs of the court and therefore a few basic ideas form their foundations. First, a record must be kept of all actions performed on evidence and a chain of custody must be maintained for all the evidence. The court requires this extensive documentation to ensure there is no tampering of evidence or negligence during an investigation that might prevent a fair trial. Also, the court does not specify a method for evidence discovery, but it does require that a commonly accepted method be used. This provides a needed flexibility for computer forensic investigations. Also, if a computer forensic investigator is going to testify during the trial, he or she must be familiar with all the evidence in the trial. The investigator
should consider all the evidence while formulating an opinion that will be express during the trial. 4.2. Preparation for testifying There are a few things a computer expert witness must do to prepare for testifying during a trial. Expert witnesses should prepare a deposition. This document will contain all the findings of the expert and any opinions that he or she will be testifying to during the trial. In some cases, the expert may be required to prove the reliability of his or her methodologies. If so, peer-reviewed sources should be used to provide a basis to defend the method or technique used to reach any conclusions [2]. It will be provided to both parties to inform them of the expert witness s findings. While preparing this deposition, the expert witness should use a great deal of care. By creating this deposition, the expert has entered his or her opinion into the court records and has become an expert witness. That means that the accountability also starts here. If the expert is negligent while preparing the deposition, he or she can be held accountable. After preparing the deposition, the expert witness should be prepared enough to present the information in the courtroom setting. The expert should also be prepared to answer questions about the findings or related material and describe how he or she reached the conclusions that were presented. This will include meeting with the attorney to discuss questions and topics of the direct examination [1]. The opposing party will try to find fault in anything that is said by the expert in the deposition or during trial [14]. The findings will only seem credible if the witness seems credible. Therefore, the witness should be prepared and confident. 5. During Trial Expert witnesses play an important role during a trial. They give their opinions about evidence and help the jury understand the information presented to them. Being an expert witness is an important duty and it should be taken seriously. To do this, the expert should not only be prepared to present his or her findings and opinions, but also be prepared for crossexamination. In order for the testimony of an expert witness to be credible, the expert must be able to stand up to cross-examination. Stanley L. Brodsky has written two books that can help experts prepare for testifying in a courtroom [1, 2]. 5.1. Expert Witness s Purpose One of the fundamental parts of a court case is the evidence. However, in some cases the evidence may not be clearly understood by the jury or a conclusion may not be evident. When this happens, an expert witness can be used to interpret the evidence. Because the expert has extensive knowledge in a specific subject area, he or she can shed more light on the evidence in question. The court allows expert witnesses to express opinions. This can be a very powerful tool for either party in a case. This can also lead to the temptation of using an expert for the wrong reason. Experts get paid for their services and may be tempted to sell their opinion. That is, they may give a favorable opinion for the party who retained them. This should not be the goal of an expert witness. Instead, experts should strive to help establish an understanding of the evidence based on the facts and not who pays them [2]. There are times when an expert may disagree with another s opinion. This is expected in any court case. Each party may have an expert that gives a contrary opinion to the other. If both experts use reliable methods to reach their opinion, it is left to the judge or jury to make a decision about who to believe [16]. 5.2. Cross-Examination Expert witnesses will testify to the opinions that the retaining party needs. However, he or she must also answer questions from the opposing party. Cross-examination can be used to help understand parts of the experts opinion that may be vague, but most often, it is used to attempt to discredit the witness. One fundamental rule to follow during crossexamination is do not change conclusions on the witness stand [1]. An expert witness should use proven methods to reach his or her conclusions and there should be no room for error. If an expert makes a mistake during testimony, he or she should correct the mistake as soon as possible. If he or she cannot correct it, then the expert should let it go and move on [1]. A good way to prevent this situation is if the expert does not know the answer, then admit it [1]. Examples of testimony, including crossexamination, can be found in A Guide to Forensic Testimony by Fred Chris Smith [12].
If the witness is not seen to be credible during testimony, then his or her opinion will carry less weight. The information that the expert is responsible for depends on the terminology used to describe the witness. An expert witness should always keep in mind his or her area of expertise and only answer related questions [1]. For a computer scientist, this can be very important. If the witness is classified as a computer expert, then he or she can be questioned about anything computer related. However, if the title is more specific, the questionable information is reduced. For example, the witness may be classified as an operating systems expert. In this case, the witness can only be asked about operating systems. By using the appropriate terminology, it can make cross-examination much easier for the expert witness. Therefore, the witness will appear more credible. 6. Post Trial When a trial is finished, expert witnesses cannot be held liable for the outcome of the trial. However, there are specific instances where an expert can be held liable. The courts try to limit the suits filed against expert witnesses, because they do not want to discourage experts from testifying in other trials. The only instance where courts will allow parties to prosecute an expert witness is when there is shown to be negligence involved in preparing a deposition or testimony. An expert cannot be prosecuted merely because a party is unhappy with the findings of the witness or the outcome of the trial. An expert witness s job is to form an opinion using accepted methodologies using the information available. If the expert witness does this, he or she cannot be prosecuted, regardless of the outcome of the trial. If the expert is found to be negligent while preparing his or her opinion, he or she can be held accountable for the negligence [10]. 7. Conclusion An expert witness provides an important service to courts. Experts should take their responsibilities seriously and carefully prepare and testify to their opinions. Court cases are increasingly involving computers and computer science experts are needed to help inform the judge and jury of issues that could determine the outcome of a case. A wide variety of computer issues may be involved in a court case. Experts should only testify to specific subject areas to which they are qualified to give opinions. By doing this, the expert s opinions will more likely be accepted by the judge or jury and the expert will likely be used again in the future. 8. REFERENCES [1] S. L. Brodsky, Testifying in Court: Guidelines and Maxims for the Expert Witness, American Psychological Association, Washington, DC, 1991. [2] S. L. Brodsky, The Expert Expert Witness: More Maxims and Guidelines for Testifying in Court, American Psychological Association, Washington, DC, 1999. [3] R. Crawford, The Expert Witness: A Manual for Experts, 1stBooks Library, Bloomington, IN, 2001. [4] ExpertWitness.com, About ExpertWitness.com, http://www.expertwitness.com/help.phtml?f=about (current 5 Dec 2003). [5] Federal Rules of Evidence, U.S. Government Printing Office, Washington, 2002. [6] L. Headlund, X-Watch: Patently False, http://www.interex.org/pubcontent/enterprise/jul99/11 xwatch.html (current 5 Dec 2003). [7] H. Kaufman, The Expert Witness. Neither Frey no Daubert Solved the Problem. What Can Be Done?, International Review of Law Computers, vol. 15, no. 1, 2001, pp. 79-101. [8] LegalExperts-UK.com, Who can be an Expert Witness, http://www.legalexpertsuk.com/menus/howtobenaexpertwitness.htm (current 5 Dec 2003). [9] E. P. Richards and C. Walter, Science in the Supreme Court: Round Two, IEEE Engineering in Medicine and Biology, vol. 17, no. 2, March/April 1998, pp. 124-125. [10] E. P. Richards and C. Walter, When Are Expert Witnesses Liable for their Malpractice?, IEEE Engineering in Medicine and Biology, vol. 19, no. 2, March/April 2000, pp. 107-109. [11] J. Robbins, An Explanation of Computer Forensics, http://www.computerforensics.net/forensics.htm (current 5 Dec 2003).
[12] F. C. Smith and R. G. Bace, A Guide to Forensic Testimony: The Art and Practice of Presenting Testimony As An Expert Technical Witness, 1 st edition, Addison-Wesley, Boston, MA, 2002. [13] J. Stuart, Expert Witnesses - Forensic Engineers, IEE Colloquium on Principles of Law for Engineers and Managers, Part 1, digest no. 1996/246, 17 Oct 1996, pp. 3/1 3/3. [14] Tips for Experts: What s an Expert Witness/Depo Preparation, http://www.lectlaw.com/files/exp01.htm (current 5 Dec 2003). [15] C. Walter and E. P. Richards, Keeping Junk Science Out of the Courtroom, IEEE Engineering in Medicine and Biology, vol. 17, no. 4, July/August 1998, pp. 78-81. [16] C. Walter and E. P. Richards, III, Using Expert Testimony in Scientific Misconduct Cases, IEEE Engineering in Medicine and Biology, vol. 14, no. 3, May/June 1995, pp. 338-341.