The presence of bruises can be time-sensitive. Generally, if someone has been grabbed or hit, they have bruises to prove it. That physical evidence proves that someone did hit you because you have punch marks on your neck or red marks around your head, for example. You are looking for any place on the body that responded to a violent touch. Sometimes the police take photographs of the other individual but never bother to photograph both people. If you have bruising around your neck, shoulders, or back the next day, then there is enough evidence to prove that they were, in fact, acting in self-defense.