I often say that when it comes to investigating cold cases, no one tells me 100 percent of the truth. This definitely applies to witness statements – and it can happen for a variety of reasons.
Sometimes, witnesses want to hide something they were doing at the time. So, for example, a guy who says he walking his dog when he saw a murder happen may have actually been doing drugs – or something X-rated with a woman who was not his wife. In other cases, the differences in detail can be down to faulty memories.
We all know that eyewitness testimony is an important part of murder investigations. But it’s not foolproof. And there are a lot of misconceptions about memory that can complicate a case. For example, experts tell us that jurors tend to give more weight to the testimony of eyewitnesses who are very confident that they are correct about their identification of suspects – even though research shows that highly confident eyewitnesses are not any more accurate than those who are less confident.
Psychologist Elizabeth F. Loftus of the University of California has stated that memory is “more akin to putting puzzle pieces together than retrieving a video recording.” The passage of time - a huge factor in cold cases - also tends to make certain memories more hazy. Over time, memories become less detailed and more broad and general. Specific details may fade away. Memories can also differ depending on who is asking the questions - and to the people the witness has talked to.
And this isn't limited to small towns: In the shooting of rapper Tupac Shakur, Las Vegas police questioned several witnesses in a parking lot. But instead of separating them, police let many witnesses stay in the same place. The result, according to former LAPD detective Greg Kading, who wrote the book Murder Rap about the case, was that many people incorporated details of other peoples' stories into their own story.
When we started trying to piece together the events of September 20, 2004 - the day Rebekah was murdered - I couldn't help thinking about the researcher who said that memory retrieval was like paleontology because "out of a few stored bone chips, we remember a dinosaur.”
Put simply, this means that if a person can't remember - they tend to fill in the gaps depending on what would make sense. To further complicate things, stress can affect memory in different ways for different people. Some people remember it better - while others find it so traumatic that they may block out certain events.
Also, Rebekah was not reported missing until September 21. So September 20 was not stressful or significant to most people present that day - other than the killer.
To help with memory, many private investigators and police detectives today are trained in the cognitive interview (CI) technique. CI was developed by psychologists in response to a request from law enforcement for better interviewing method - and it's also something that many investigators use on a daily basis.
The idea is to make the witness as comfortable as possible by asking open-ended questions rather than “yes” or “no” questions. Witnesses should be encouraged to recall as much detail as possible, even if they recall events out of order or the details seem trivial.
As an investigator I have sometimes had to listen to hours of seemingly unrelated stories - but trivial details can be massively helpful later. We ask questions like "What was the weather like?" to trigger memory, or try to start at a point that the witness does remember and work backwards. It means letting them talk - and actively listening.
And it works. According to research, new witnesses can be the key to cracking cold cases – even more than DNA evidence. Forensic science may get sexier headlines, but old-fashioned investigative work is what matters the most in many homicide cases.