Why are eye witness accounts so unreliable? This is because memory is extremely susceptible to suggestion and emotions and social pressures weigh a lot on how we remember things. In a 1974 study published in The Journal of Verbal Learning and Verbal Behavior, Elizabeth Loftus, a psychology professor at the University of California, Irvine, conducted a study in which she asked participants to watch clips of several fender benders in which no glass was broken. The participants who were asked what happened when the cars 'smashed' into each other were much more likely to say glass was broken than those who were asked about when the cars 'hit' each other.
In 1999 researches at Harvard conducted a study in which they asked participants to watch a video of people dressed in all white and all black pass a ball. They were asked to count how many times the players in white passed the ball. During the video a person in a gorilla suit walked through the court and more than 50% of participants didn't report seeing it. The conclusion is that in a court of law witnesses are instructed to tell nothing but the truth. And they think they are telling the truth, but the reality is that their truth is constructed and not based on facts.