I worked as a bank teller when I was younger and it was pressed upon all employees with great emphasis that if we were ever robbed not to talk about it with anyone until talking to the police. Why? Because under stressful situations people don't remember accurately and tend to change their minds without even realizing it and start to say they saw what someone else saw, or describe a person wrong, or their ideas of what match those around them. So witnesses in a stressful situation who have had time to sit around and talk to each other before the police I don't think can be trusted. I've seen people describe a completely different person and circumstance after a crime happened because their minds molded to what they were hearing, like a game of telephone the message at the end is completely changed. .