Normally... Front Car is not at fault unless they did something malicious or downright stupid... Middle Car is at fault for hitting Front car. Back car is at fault for hitting Middle car. Quite often they'll ask the Front car if they felt 1 hit or 2 hits. If 1 hit, the collision order was Back->Middle, then Middle was pushed into Front. If 2 hits, the collision order was Middle->Front, then Back->Middle. Either way, Back car is normally found at fault... the only difference is if the Middle Car is also considered at fault (aka. Did they stop in time)