A police officer friend told me once, that 'eyewitness accounts are almost useless, most of the time'. They almost always conflict and most if not all of the accounts, are filtered through the eyes of the witness's own set of preconceptions. In short, if twelve people all witness the same event, and then have to repeat what they saw to a third party, the interviewer after the fact, will invariably receive twelve different accounts of the same event.