My cousin got beaten up by US Marines?

So it was this morning. He's like 14 and like a gang of five Marines were driving by the neighborhood with their truck. They were going really fast and weren't looking. My cousin was crossing the street and they were going so fast that they had a sudden stop. One of them yelled at him and called him an a$$hol€ and dropped the f-bomb. But my cousin gave them the finger and threatened to tell because they were driving above the speed limit. So that one Marine dude got out of the car and started punching him about five times by the time he was done, my cousin had a bruise on his upper left cheek. They left, and we were just standing there, what do I do now? I haven't told anyone the truth yet, we both told his parents that he ran into a pole but it started to hurt real bad, oh and did he deserve it ir not?