Tuesday, September 25, 2012

How to Write a "Bad" Expert Witness

by Tom Adair author of The Scent of Fear (2012)

One of the most interesting observations I have made in the courtroom is what passes for an "expert witness". In the United States, judges act as "gate keepers" for the admissibility of scientific evidence and expert testimony. The legalese can get pretty convoluted but in the end the judge can pretty much rule any way they want and let the jury decide how much "weight" they prescribe to the evidence or testimony. Also, in the US the burden of proof is on the prosecution and some judges give a bit more latitude to the defense in terms of whom they offer to testify for their client. I know of one case where an "expert" in entomology was allowed to provide expert testimony in a murder case. Their qualifications? They worked at the local zoo and raised insects to feed to the reptiles.

At times throughout my law enforcement career I have worked as an independent expert for both the prosecution and defense. Defense experts sometimes get a bad rap in my opinion just because they work for the accused. In truth, there are some really good experts out there whose only allegiance is to their analysis. However...there are some "experts" who may not follow a strict ethical code. When you come up against one of these folks it can get really frustrating. They may seem very credible to a lay jury, judge, and even the attorney unless someone is there to point out the inconsistencies. As a writer, understanding how these experts behave can add some real texture to your dialog and storyline.

One of the biggest tells is their tendency to set standards for others that they themselves do not meet. They love to make grandiose statements about how investigations or analyses should be conducted.  In one case an opposing expert said that a "good investigator" reviewed every single photo and every single piece of evidence in a homicide. He sat up on the witness stand with a semi-large photo book so I had the prosecutor ask him if those were the photos (provided by defense) that he had examined and then had him count them. Long story short he had reviewed only 10% of the photos taken at the crime scene. I then had him review the evidence log showing which items of evidence he had checked out for his examination. This time it was less than 5%. So in a few questions he confirmed though his own definition that he was a "bad" investigator and his testimony was largely ignored by the jury.

Sometimes it is not the expert but the attorney that lays the groundwork. They may attack the opposing expert for not having enough training, experience, or certifications. They basically set the bar very high for the opposing expert. However, they don't consider (or maybe they hope no one else will) whether their own expert meets those same standards. So you could have an attorney challenge an expert on the basis that they lack a board certification in a particular forensic science field. Of course, when their expert takes the stand and lacks the same qualifications the jury is left wondering just how seriously the attorney believed what they said.

In another case which happened about a decade ago an expert claimed that a new DNA process (and machine used to do the testing) were unreliable and shouldn't be considered by the court. The opposing attorney called the manufacturer to provide a rebuttal and imagine their surprise when they discovered that the expert in question had bought one of the units for their practice at the cost of over $80,000.00! They had even used it for examinations in other cases and never once mentioned their hesitation to use the technology when testifying in those cases. So the opposing attorney simply asked something like "why would you spend so much money on a technology that you claim is unreliable and then use it in other cases?"

It has been said that a courtroom is two thousand square feet surrounded by reality. In truth, each side is allowed to advocate their own position and interpretation of the evidence within certain rules and guidelines. This reality leave a lot of wiggle room though. A good attorney can convince a jury of the absolute truth of their claim. That is, until the opposing attorney takes the stage. Trials can seem like a roller coaster ride going up and down and upside down. Your experiences range from nausea to unmitigated joy. I thing that is the essence of good writing too. So if you are writing a courtroom scene don't just settle for a he said, she said type of exchange. Give your characters some secrets or positions they can't possibly maintain. After all, that's what the "experts" do.


  1. Thanks again for your insight. I love the details. I haven't written any courtroom scenes yet, but I like courtroom thrillers, and I know I will write such a scene eventually.

    I was surprised to learn that such questionable "experts" were allowed to testify. I suppose as long as the other side has the list of witnesses beforehand and does their homework, the damage can be mitigated.

  2. This information seems both frightening and interesting.

    As a private citizen, it scares me to know incompetence can slip so easily into a courtroom where people's futures are at stake.

    As an author, however, it opens new possibilities as I plot my novels.

    An interesting, detailed, and informative post, as always.

  3. This is great, Tom. I totallly appreciate the details and personal anecdotes you have. Fabulous!

  4. As an expert witness myself (in the field of handwriting) I've seen some "experts" on the stand lying about their credentials and being accepted, all evidence to the contrary. Pretty scary.

  5. Thanks everyone. I guess I see both sides of it to some degree. I know it can be a little strange to think these folks make it past the gatekeeper but on the other hand the judge needs to ensure that the defendant has the right to choose their own witnesses. Most of the time the bad ones are brought into the light on both sides but once in a while I suppose they get away with it.

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