St. Louis County Prosecuting Attorney Bob McCulloch announced on Monday the grand jury's decision not to indict officer Darren Wilson for fatally shooting 18-year-old Michael Brown. (AP)

The somber, gray-haired prosecutor stood before throngs of cameras on Monday night and considered the many problems that plagued the investigation into the killing of unarmed teenager Michael Brown. There was the media, he said, and “its insatiable appetite for something, for anything to talk about.” Then there was chatter of social media and its “nonstop rumors.” And finally, there were the dozens of witnesses, many of whom remembered conflicting versions of the same events.

All claimed to have seen the final moments of Brown’s life, St. Louis County Prosecutor Robert McCulloch said. They all claimed to have witnessed Ferguson cop Darren Wilson pump bullets into the youth. But that’s just about where the similarities ended. And soon, as investigators sank deeper into a controversy with national implications, it was difficult to parse who saw what and who saw anything at all.

“At least one witness stated that as Officer Wilson got out of his vehicle, he shot Mr. Brown multiple times as Mr. Brown stood next to the vehicle,” McCulloch said. “Yet another witness stated that Officer Wilson stuck his gun out of the window and fired at Mr. Brown as Mr. Brown was running. One witness stated there were actually two police vehicles and four officers present, but only one officer fired a weapon.”

Of all the tools at an investigator’s disposal — DNA analysis, forensic evidence, witness testimony — by far the least reliable are the recollections of witnesses, studies suggest. More often than not, they raise more questions than they answer and sometimes produce deeply flawed cases.

“Surveys show that large proportions of people, at least in the United States, think that human memory works like a video tape or a DVD,” Scott Lilienfeld, an Emory University professor who has studied the shortcomings of such testimony, told New York Magazine. “And we know of decades of psychological research that human memory, including eyewitness memory, doesn’t work that way.”

It works even less when it turns out that an “eyewitness” didn’t witness a thing. That happened in testimony before the grand jury that investigated the Ferguson killing, said McCulloch. Some described what happened at critical moments, he said, only to concede “in subsequent interviews” or testimony that they didn’t actually see what they were describing.

It’s not a matter of people lying, he suggested. Asked by a reporter if he was contemplating perjury charges against any witness, McCulloch answered with a definitive no. “I think they truly believe that’s what they saw, but they didn’t,” he said.

On Ferguson’s streets, rumor begat rumor. “Some [eyewitnesses] were running for cover, some were relating what they heard from others or, as I said, what they assumed happened in the case,” he said.

McCulloch’s remarks were by no means the first indictment of eyewitness testimony, which has come under increasing suspicion in the past generation as innocent men, sent to prison by incorrect witness identification, are exonerated. The human mind is a malleable thing. More so memory.

“The most common element in all wrongful convictions later overturned by DNA evidence has been eyewitness misidentification,” according to the Innocence Project, which works to exonerate people it believes have been wrongly convicted of capital crimes. In fact, in the past few decades, 73 percent of 239 convictions overturned through DNA testing were because of faulty eyewitnesses, Scientific American reported. “One third of these overturned cases rested on the testimony of two or more mistaken eyewitnesses,” Hal Arkowitz and Lilienfeld wrote in the article. “How could so many eyewitnesses be wrong?”

Simple, found Scientific American. And many of the reasons can be seen in Ferguson. They include: “extreme witness stress at the crime scene or during the identification process; presence of weapons (because they can intensify stress and distract witnesses); [and] a racial disparity between the witness and the suspect.”

When it comes to memory, there are all kinds of opportunities for mistakes. What your friends say can skew what you think you saw. What the TV says can skew what you think you saw. What you wanted to see can skew what you think you saw. So witnesses plug memory’s holes with assumption, wrote Barbara Tversky in the Stanford Journal of Legal Studies. It’s human nature.

“Reliance on assumptions are necessary to function in our society,” she said. “…We are constantly filling in the gaps in our recollection and interpreting things we hear. For instance, while on the subway, we might hear garbled words like ‘next,’ ‘transfer,’ and ‘train.’ Building on our assumptions and knowledge, we may put together the actual statement: ‘Next stop 53rd Street, transfer available to the E train.’ Indeed, we may even remember having heard the full statement.”

But those hypothetical people didn’t hear the full statement. They just think they did.

And once an inaccuracy becomes part of a person’s recollection, it’s almost impossible to dislodge. Even when that person, Tversky wrote, is challenged with direct information that refutes his or her own memory. “Once witnesses state facts in a particular way or identify a particular person as the perpetrator, they are unwilling or even unable — due to the reconstruction of their memory — to reconsider their initial understanding.”

This appears to be what occurred in the Darren Wilson investigation. Even when authorities challenged witnesses with forensic evidence — which McCulloch said “does not change because of public pressure or personal agenda” — they didn’t back down. He gave as an example witnesses who said they saw Wilson pump bullets into Brown’s back, sticking with their story even after autopsies demonstrated that no bullets entered Brown’s back.

They “stood by original statements even through their statements were completely discredited by the physical evidence,”  McCulloch said.

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