don't loss the eyewitness

get all his information, like telephone number...

find a lawyer, tell him that you probably can secure a eyewitness and ask the probability to win (I guess you will not sue him, but rather defend yourself).

don't worry about assets now... the first step is to find a lawyer specializing in personal injury cases (Tort)...has to know how to do litigation, both procedural rules and substantive rules.