There are 2 types of bullys.
Type 1. the insecures.
this type of bullys feels insecure, they need to feel superior and accepted so they usually go in big groups from 3 to 10 (usually). to feel superior they bully people, they make them feel bad and just like this little piece of tauroscrap did with you they try to do wathever they can to hurt others.
type 2. the egocentric ritch kids.
this type of bullys always feels superior. their ego haevs the same prize as their moms, they dont care. all they want is to be a "bad boy" and they just bully to have fun. there is no specific reason to do bully for them, just for fun. they go in little groups of similars, they dont need a big group. they are usually pretty good making "friends" that they use to have fun, thats how the 25% of their victims are their "friends". The egocentrc ritch kid bullys also uses to have some hints of being psychos.
with this i try to say that he did it because he wanted to feel better because hes just a little peace of tauroscrap. no other reasons, hes just dumb. and btw im usre you already know that you are for sure good gyt, i dont know you but man you acted in such beautifull way... i mean you did just what you had to do. you called the police and acted fast. good job, if i where your dad/mom i would be proud of you