Just ask them what they saw. After you have accumulated the statements, made all your measurements, taken photographs, and filled in the blanks on your crash report, you get the scene cleared and go back on patrol or head off on another assignment. Maybe there is still a lot more investigating to be done, or perhaps you need to do some reconstruction. This involves vehicle damage analyses, preparing scale diagrams, mathematical computations, and so on. You do the best you can.
Witnesses often discuss their views of the event with relatives.
They read newspaper stories and watch TV coverage of the incident. Sometimes, after seeing or reading about an accident, witnesses you never heard of call the station to report what they saw. Researcher Henry Roediger, at the American Psychological Association, said that experiments with college students at Rice University in Houston indicate that it's quite easy to introduce false memories. Later, when asked what they'd seen on film, they reported the version they'd read. California psychiatrist Lenore Terr says that terrifying incidents are particularly susceptible to memory mistakes because the horror and confusion interferes with the memory process.