When you are deposing the other side’s expert witness, preparation and consideration of strategy are essential components to success. Areas of attack include:
- The integrity of the evidence
- A particular scientist’s work
- The conclusions of the scientist
- Competence of the scientist
- Challenges to the science itself
- The reliability of the laboratory in question
- Finding common ground
Not every line of attack will be appropriate in every case, so careful consideration must be given to the theme of each case. Attorneys should consult with an expert of their own prior to deposing the expert for the other side. Attorneys should consider each potential line of attack, and, where appropriate, gather publications which support their theory, or, in the alternative, weaken the opposing expert’s position.
Challenges to the Integrity of the Evidence
In science, if it isn’t written down, it didn’t happen. Consequently, good scientists document their work, from the time they receive the evidence to the time the evidence leaves their possession. Sometimes, the best challenge to expert witness testimony involves a lack of care exhibited by law enforcement in collecting the evidence in the first place.
For Unsealed Envelopes
- In reviewing your notes, I see the evidence arrived at the laboratory unsealed. Does the lab accept unsealed evidence?
- Your notes indicate the law enforcement officer was asked to seal the evidence, is that correct?
- Why does the lab refuse to accept unsealed evidence? (Or, isn’t it true that the lab doesn’t accept unsealed evidence because of the possibility of evidence contamination?)
For Contaminated Evidence
- Your notes indicate the evidence envelope was “red stained” on the outside. Fair to say you found this unusual?
- You took the time to note this because you found it relevant?
- In every case, part of your protocol includes documenting the condition the evidence arrives in
- And in this case, the evidence arrived at the lab in a manner you found unusual?
- Would you agree with me that envelopes that are “red stained” might be stained with blood?
- And such staining could result in contaminating whatever is inside the envelope?
- Does it also suggest poor evidence collection practices at the scene?
- Is there any way to determine if a piece of evidence was “red stained” when law enforcement arrived on the scene, rather than after it was collected by law enforcement?
- It is possible law enforcement contaminated any or all of the evidence during the collection process? (Note: take the time to review the photos, if there are any, before asking such a sweeping question. It is possible the photos will establish at least some evidence was blood stained when law enforcement arrived.)
For Evidence Without a Valid Chain of Custody
- Your notes describe the condition the item was in when it arrived at your laboratory. But can you describe the condition it was in when located?
- Can you presume to know the condition it was in when it was located?
- Do you know if the condition of the item was altered between the relevant time frame and the moment it was located?
- Do you know if the condition of the item was altered between the time it was located and the time it arrived at the lab.
Challenges to a Scientist’s Work
When challenging a scientist’s work, lawyers question the method the scientist used when analyzing the evidence. Any time more than one generally accepted method of analysis exists, this provides a viable line of questioning. Lawyers must keep a tight rein during this line of questioning. Scientists, like other human beings, believe they made the “right choice” when they analyzed evidence. If given an opportunity, they will take great pains to justify their choices. Additionally, it is rare to have a case in which everything available for testing is actually tested. In the right case, choice of method may provide a valid line of attack
Choice of Testing Method
- I see you examined the evidence using Gas Chromatography and Mass Spectrometry. However, there are other methods a scientist could employ to examine the evidence, aren’t there?
- For example, High Performance Liquid Chromatography (HPLC) is another method you could have used, isn’t that correct?
Choice of Evidence
- The notes you took indicate law enforcement sent you six items of evidence. Did you know law enforcement actually gathered 19 items of evidence?
- And you didn’t test any of the evidence that wasn’t forwarded to the lab?
- If you had received that evidence, could you have examined it / performed testing on it?
- Of the six items of evidence you received, I note you only tested items 2 and 4. Is that correct?
- So even though they were in the laboratory, you didn’t test items 1, 3, 5, or 6?
- If you had tested those items, you might have discovered additional evidence.
Challenges to the Scientist’s Conclusions
Directly challenging a scientist’s interpretation of evidence may be difficult without the assistance of a qualified expert of your own. However, where you are dealing with a subjective discipline, you may have some success. Sometimes, this approach goes hand in hand with the “finding common ground” technique. Some examples are below.
- Is it true there is disagreement in the forensic science community about how to interpret forensic DNA mixture profiles?
- Would you agree with me that other scientists may look at the same mixture and come to a different conclusion?
- You examined a spent cartridge casing found at the crime scene, and compared it to cartridges test fired from the gun found in the defendant’s house?
- You concluded the cartridge casing at the crime scene was fired from the gun found in the defendant’s home. And you base this conclusion on your training and experience?
- But your training calls for your judgment, based on whether you believe there is “sufficient agreement” between the markings on the cartridge casing.
- After such an exam, your conclusions could be “match,” “no match,” or “inconclusive,” correct?
- Fair to say another firearms examiner might come to a different conclusion?
- And that’s because this is a subjective science?
Challenges to the Scientist’s Competence
Forensic scientists must take a competency test before they can begin casework in any accredited laboratory. Additionally, forensic scientists must take and pass proficiency tests at regular intervals. Finally, when a forensic scientist makes an error which someone subsequently discovers, the lab documents the error. However, unless the error was made in the case at issue, or you ask for it specifically in discovery, it is unlikely you will have knowledge of it.
Attorneys should explore any failed competency test or failed proficiency test at length. Additional sources of information about the scientist’s competence can include the employee file, as well as their proffered curriculum vitae.
Challenges to Proficiency Tests
- You take proficiency tests to establish ongoing competence in the discipline?
- But proficiency tests are not exactly like case work, are they?
- For example, proficiency tests have a known answer.
- Proficiency tests are not as complicated, generally speaking, as casework.
- You spend as much time as you want on a proficiency test?
- You know someone will check your answers when you take a proficiency test?
- And despite the fact you knew you were being tested, despite the fact you had as much time as you wanted, and despite the fact the test was designed with a known, specific answer, you still failed the test?
- In reviewing the test results from this proficiency test nationwide, it had a 97 % pass rate.
- Further, in reviewing the test results for this proficiency test in your laboratory, all the other scientists passed this proficiency test, is that right?
Challenges based on Other Scientist Errors
- In June of 2016, your DNA contaminated a sample, is that correct?
- Your lab did a root cause analysis of this contamination event?
- Your plan was to wear a mask in the future, while performing DNA testing.
- In looking at the protocol for DNA testing in the laboratory in June of 2016, I see wearing a mask is already part of the protocol, isn’t that correct?
- Yet, it appears you weren’t wearing a mask when you contaminated the sample?
- Additionally, your DNA profile appeared in another case in August of 2016.
- Again your laboratory did a root cause analysis.
- Again, your lab made a plan that you would wear a hair net, a mask, and gloves in the laboratory when doing testing.
- In reviewing the DNA protocols in place at the time, masks, gloves, and hair nets are already mandatory. Were you unaware of those requirements or did you simply choose not to follow them?
- Finally, you had created a plan in June of the same year to wear a mask while doing testing, yet in August, you failed to follow your own plan, isn’t that correct?
Challenges Based on Corrections Made After Review
- In August of 2017, you were part of the team that arrived at the scene of the fire.
- Your job was to sketch the scene, to scale.
- Did you do that?
- After you did that, did you provide the sketch to your supervisor for review?
- Did your supervisor have some changes for you?
- They included adding a set of stairs on the back of the house, which you had omitted?
- In reviewing the protocols for drawing a fire scene, isn’t including things such as points of entry, including stairs, a part of the process?
- Yet you failed to do so in your initial drawing?
- The corrections also included adding a symbol indicating North?
- In reviewing the protocols for drawing a fire scene, isn’t including a symbol indicating North part of the process?
- Yet you failed to do so in your initial drawing?
Challenges Based on Background
- I see you don’t have a college degree in fire science.
- In fact, I don’t believe you have any formal schooling in fire science.
- Are you aware best practices include having formal education in fire science?
- In fact, the National Fire Protection Association NFPA 1033 calls for post secondary education in fire science, fire chemistry, and fire dynamics, just to name a few?
- You don’t have any post secondary training of that type?
- Instead, your training came from other fire investigators?
- In reviewing your resume, I see you haven’t attended any Continuing Education in your field in the past year?
- You haven’t taught any courses to your peers regarding your subject matter expertise?
- Additionally, you haven’t published any papers in peer reviewed journals in your area of expertise?
- Finally, you haven’t published any books on the subject?
Challenges to the Science Itself
Many forensic science disciplines have been subject to criticism over the last decade. Of particular use to an attorney are the publications Strengthening Forensic Science in the United States: A Path Forward, published by the National Academy of Sciences, and Forensic Science in Criminal Courts: Ensuring Scientific Validity of Feature-Comparison Methods, issued by the Executive Office of the President, President’s Council of Advisors on Science and Technology. Both reports contain sharp criticism of forensic sciences, particularly of so called “pattern evidence.”
- Bite mark analysis involves examining marks left on the victim in this case?
- And you compared that to the dental impressions from my client?
- Your comparison relies on the premise dental characteristics vary substantially between people?
- And further, that skin can reliably capture these distinctive features?
- First you determine whether human teeth caused an injury?
- Is it fair to say each step of the process is subjective?
- There are no generally accepted protocols that include well defined standards about the identification of features that constitute a bite mark from human teeth?
- There is no protocol about the degree of similarity that must be identified to support a conclusion a bite mark matches a certain person’s dentition?
- Instead, each examiner relies on their own judgment in making their conclusion?
- Studies have shown false positive rates with bite marks?
- In fact, studies establish various bite mark practitioners cannot consistently agree on whether an injury is attributable to a human bite mark?
Challenges to the Reliability of the Laboratory in Question
In some cases, challenging the laboratory itself is fruitful. In this day and age, where lab scandals are a dime a dozen, there may be an area of cross exam based on a bad laboratory practice. Most labs are accredited, and if they are not, this should be explored. Even when a lab is accredited, this should not be the end of the analysis. Review the accreditation documents, including the preliminary report, which comes before the final report. The preliminary report includes a laundry list of errors and omissions the lab must fix before the final visit.
- I see your lab most recently obtained re-accreditation in 2017.
- However, I note, during the accreditation process, evaluators discovered the reagents in the drug chemistry section expired but remained in use.
- Would you agree with me the drug chemistry section shouldn’t be using expired reagents?
- Yet, the drug chemistry section was using expired reagents.
- In fact, they might still be using expired reagents if the accrediting body hadn’t discovered the error.
- Does your lab have protocols in place to prevent using expired reagents?
- If not, don’t you think that would be a good practice?
- If so, why wasn’t the protocol followed?
- Your lab was in the news about a year ago, regarding one of your lab’s scientists.
- She was claiming in testimony she had a master’s degree in chemistry, which she didn’t actually have. Are you familiar with this case?
- Does your lab simply accept the cv’s the employees submit without checking them for accuracy?
- If her cv was correct, but she was lying in testimony, how come this wasn’t discovered? Doesn’t your lab monitor testimony, as required by the accrediting body?
- Why wasn’t this deception discovered earlier?
Finding Common Ground
Sometimes the best approach involves finding common ground where you and the opposing expert can agree. For example, if the expert concludes there is evidence of gun shot residue on the deceased’s right hand, thus consistent with suicide, and your case is predicated on suicide, you may not wish to examine the witness about the ease of transfer of gun shot residue, or law enforcement’s failure to collect a substrate from another surface on the body for comparison, because surely if the victim was shot from close range, there’s gunshot residue on the victim, regardless of whether she or someone else pulled the trigger.
When the analyst’s conclusions are consistent with, or at least not in direct conflict with your theory, finding common ground is the best approach, even if you know there are legitimate challenges you could make to the scientist’s conclusions. In this case, you work to make the expert your own.
- I notice from you cv you have 23 years of experience in gunshot residue cases.
- In this case, your examination revealed the presence of gunshot residue on the woman’s right hand?
- This is consistent with her having fired the weapon, isn’t that correct?
- Your examination revealed the presence of sperm on the vaginal swab?
- And the DNA test results match the DNA profile of my client?
- Can you tell, by looking at the sperm under the microscope, whether the woman consented to sexual intercourse?
- Is there a scientific method of examining a forensic DNA profile which determines whether the DNA was deposited consensually?
- So while you can testify you found a DNA profile consistent with my client, there’s no way for you to tell, scientifically, whether a crime occurred?
This article does not address questions involving Daubert or Frye, as those are topics for another day. Instead, these questions seek to provide you with a starting point for various lines of attack on the opposing side’s forensic expert. Lawyers should discuss these questions with their own expert. Additionally, attorneys should review questions with colleagues, confirming well crafted, understandable questions asking only for bite sized pieces of information. Even if you are yourself an expert in a given forensic discipline, the same cannot be said for the jury or the judge. Attorneys should approach deposing scientists taking baby steps, introducing facts slowly and methodically.