Stilled on a Train

During a train ride, someone is killed: an unnamed father character.

WHO IS THE KILLER?

Timmy: the child of the killed and inheritor to his fortune?

Jimmy Bob: an insane business rival?

Killer Robot: a ... killer robot? (There is not much else to say about this one...)

James T. Wisters: a greedy man seeking to boost his income?

The conductor: the guy who runs the train while waiting for a package from his aunt?

Or could it be...

YOU!!!!

(I'll give you 2 hints: it's not you or the conductor.)

Please leave a comment on who you think it is, and why.