When you kill somebody while driving within speed limit it is an accident.

When you kill somebody while driving above the speed limit it is a Crime even when you exceed by 5 mile.

Accident can happen from anybody's car.But we should always follow the law or that country where we live. Dont exceed the speed limit .   Doesn't matter what other person do and how they drive. Just don't drive exceeding the limit  . And of course don't run away from the cops.  Just by following the law you yourself are putting in much better position even when you meet an accident.