School thief keeps trying to steal my iPhone?

Now let me give you some info about this thief. Lets call him Jesus Lopez. About a year ago, I lent him my Gamecube (which I never got back). After 6 months, I ask him if he sold it, he actually confesses and some girls overhear this conversation. They told me that Jesus stole their phones. Now back to this day, he tries to make his move on me once again. I was listening to music on my iPhone, Jesus saw it and asked if he could borrow it. Obviously I said no, but he kept trying to make me crack. Then he finds he has no other way to get it, he tries to rip it out of my hand, but I know martial arts, so he was unsuccessful. Then he tries to talk me into it, which I'm saying no everytime. I had to get him to give up, so I smooth talked him into leaving me alone. He walked away, but later asked me again. I declined, but he tried to use force again. I get him off of me an manage to get away. I have a feeling he will ask again. What should I do?

Report everything to the school authorities.

Tell the school authorities, tell them you are uncomfortable being around him and he is trying to use force to take it from you.