 They carefully document the scenes of crashes, ideally in a manner thorough enough to allow specially trained officers to reconstruct the scene at a later time, after the roadway has been reopened.This includes documenting the precise details of the roadway on which the fatality occurred; the state of any vehicles involved, including the use of safety features; the condition, legal status and attitude of the operator or operators of any vehicles, and any other local factors such as the weather and the presence or absence of appropriate road signage.In addition, investigators will conduct interviews with drivers and witnesses to assist in building up an overall picture of what led to the crash.