Most of the time the answer to this question is clear. Sometimes it’s not, and sometimes more than one party can be responsible for an accident. Rear-end collisions are almost always the fault of the party hitting the auto in front of them. However, if the person slammed on their brakes for no good reason, they may be partially at fault as well.
When it’s unclear who caused the accident, cases usually become more difficult. In a situation like that, you want to document the facts and gather evidence quickly so that it can be figured out.