John Wixted

And this is happening at a time when the witness is actively thinking about the crime.

So even if the witness says, no, that's not the guy who did it,

This is how the innocent suspect's face first becomes associated with the crime in the witness's memory.

That's contamination.

You can't keep that from happening, and you can't put the witness's memory back the way it was.

So focus on the first uncontaminated memory test early in the police investigation, not the last thoroughly contaminated test that happens at the criminal trial one, two, or even three years later.

Unfortunately, courts tend to do the reverse, placing their faith in the last test of memory at trial while all but ignoring the critical first test.

This is a seriously underappreciated problem.

Well, with that in mind, let's take a closer look at how the police conduct that all-important first test of a witness's uncontaminated memory.

In the days or weeks after a crime, the police might find a suspect, a person who they think may have committed the crime, and they'd like to show them to the witness to see if they have the right guy.

They could just hand the suspect's photo to the witness and ask, is this the guy who did it?

The problem is that would be suggestive because it would reveal to the witness who the police think may have committed the crime.

To test memory in a less suggestive way, the police will often show the witness a whole set of six photos

It's called a six-pack photo lineup.

One photo is of the suspect, and the others are of similar-looking individuals who the police know are innocent.

That way they can still show the suspect's photo to the witness, but without revealing who they think committed the crime.

It's a much fairer way to test memory, and it becomes fairer still when other recommended practices are followed.

such as letting the witness know that the perpetrator who they saw commit the crime may or may not be among these photos.

And the officer who's administering these photos to the witness should not even know who the suspect is to avoid unintentionally influencing the witness's choice.

When it's done this way, it becomes a pure test of the witness's memory.