What's in a memory? All too often, experts say, much more than recollections of actual events.
As University of Washington psychologist Elizabeth Loftus writes with co-author Katerine Ketcham in Witness For the Defense, memory is not "preserved in stone, but a living thing that changes shape, expands, shrinks and expands again."
Loftus points out that coaxing the public for eyewitness testimony related to the highly publicized string of sniper shootings in the Washington, D.C., area is a gamble.
By providing the public with details from other eyewitness accounts — such as sightings of a white van with a ladder rack and a white box truck — police hope to trigger the memories of people who were near the shooting sites. But Loftus says offering such information can also "contaminate" the memories of others and make good eyewitness accounts turn bad.
Montgomery County, Md., police Chief Charles Moose and other investigators are nonetheless urging people who may have any information related to the string of 11 sniper shootings to contact police.
The chief said he realized it was hard to get strictly accurate accounts from people who may not have been paying much attention before an incident occurred.
"No one knows how to be a witness," Moose recently told reporters. "We have to train people to be a witness."
Can people be trained to be good witnesses? Although studies have shown that training generally can't improve memory recall, specialists in eyewitness testimony say there are things people can do to provide more accurate witness testimony.
Steps to Better Recall
The first rule in making a memory more accurate is to record it — as soon as possible.
Gary Wells, a psychology professor at Iowa State University who has studied eyewitness testimony for 25 years, suggests carrying a notepad and pen or a voice recorder at all times. This can help ensure that people who happen to be near the scene of an incident are prepared to record details.
Ideally, Wells says, some eyewitnesses might have video camcorders handy and can record events around them. But even scratching a license plate number in the dirt with a stick can work, says Wells.
The sooner memories are recorded, the less chance they will be warped by hearing the accounts of others.
"What's important is to externalize your memory as soon as possible because memories fade and change very quickly," he says.
Another key rule, Wells says, is to try to suppress the instinct to focus on the victim. The rules of physics dictate that by focusing on the victim of a shooting crime, a witness turns away from the victim's shooters and any traces they might leave behind.
"The weapon used in these shootings appear to be some distance away," says Wells. "So the idea is to do what does not come naturally and to look in other directions."
Loftus points out that this can be difficult for people witnessing traumatic incidents. Studies show that seeing stressful events like a person being shot can cause people to tune out peripheral details, such as the license plate of a nearby car.
It also may be difficult for eyewitnesses to follow a third rule — to resist the tendency to look for expected details. In this case, it may mean resisting the urge to look for a white van leaving the scene of a shooting. Instead, some advise it's more helpful to objectively take in as many details as possible. Often critical clues lie in descriptions that were not expected.
"Don't wheel around and look for a white van," says Wells. "First, because we don't know yet that the white van idea is right. Secondly, because there are a lot of white vans around and the sniper may be less likely to use a white van now."
Gregg McCrary, a former FBI profiler, has pointed out that in a serial murder case he was working on, eyewitnesses reported seeing two men in a beige Camaro. When the case was resolved, investigators found the suspects were actually a man and a woman traveling in a gold Nissan.
There are different theories on the best way to remember a suspect's face. A study by Garrett Berman at Roger Williams University in Rhode Island found that people are better at recalling faces when instructed to look at the whole face and noting how facial features relate to each other. People who are told to take note of individual facial features proved less successful at identifying faces later.
Wells suggests it may be useful for witnesses to make a mental note about other people the suspect may resemble. That kind of immediate comparison may be easier to recall later, he says.
The emergence of DNA as a critical part of forensic investigations has revealed eyewitness testimony to be seriously flawed. Among the more than 100 innocent people exonerated by DNA evidence in recent years, the most common cause of wrongful convictions has been mistaken eyewitness accounts.
"We have to bear in mind that memory is a fragile thing," says Loftus. "You can't overly embrace every account just because it's confidently expressed."
Eyewitness accounts may often be imperfect, but investigators say they are usually a vital part of solving a crime. And in an investigation that is proving difficult to solve, police are urging people not to be afraid to step forward with information.
"We want people to stay in the area, calm down and think about what they've seen," Moose told reporters on Tuesday. "They should not feel they're being questioned because they did something wrong, but because they can help."
The FBI's Washington field office is urging people with any relevant or timely information (not "theories, opinion or unrelated information") about the sniper shootings to call (888) 324-9800.