At trial, an expert witness is called to testify about issues “beyond the ken” of the jury, using his or her experience and background to explain things a typical juror wouldn’t understand. Experts may be called in almost any field, from police or custody practices to human resources to gangs, economics, medicine, or psychology, to name only a few.
When an expert testifies, ideally the focus should be on their background, qualifications, and opinions in the case. But sometimes the expert has something negative in his/her history that may prejudice the jury if it’s revealed. Some examples of an expert’s colorful history include: a use of force expert who tased an attorney as an experiment, another force expert who was accused of egregious sexual misconduct at his workplace and resigned in lieu of termination, and a medical expert who was sued for malpractice and had his license briefly suspended.
If you’re on the opposing side, tactical use of such information may be a key component of your strategy for impeachment of the expert witness. You will need to link the misconduct of the expert somehow to his/her qualifications or judgment in order to use it. If the attorney who retained the expert is aware of the misconduct, s/he will either move in limine to exclude it, make sure the expert has a good explanation ready to explain it, or hope that the question(s) won’t arise. This last strategy is a risky one and can result in the evidence being introduced and/or at least the damaging and leading question arising, which is often nearly as prejudicial.
How do you avoid this situation from occurring with an expert that you retain? First and foremost, vet your expert witnesses carefully. Ask them about past and problematic issues, and ask around about them. Typically the experts testifying on discrete topics such as use of force or human resources issues travel in relatively small circles and their histories are known. Second, if you find out about past misconduct of your expert after s/he has been retained, you must discuss it with your expert to decide if the issue can be adequately explained to a jury without affecting their impressions of the expert. If the information is too prejudicial, and likely to be admitted at trial, you should de-designate the expert and find a new one if possible or decide to proceed without the expert.
As the above situations illustrate, having all of the pertinent information about the expert witnesses on both sides of the case is critical. If you retain counsel, make sure you provide them with information about any potentially damaging incidents of expert witnesses. Keep files or logs with information about expert witnesses and share it with others who defend government agencies and law enforcement.