you know what. now that i think of it. i think it's his father..

this is how i see it:
banks sees some guy get shot, the killer (unknown) laughs, and drives off
later banks goes to his father and asks about it, but his father didnt know anything
last couple lines is confusing, it either means:
1) banks tells his father about the murder, and says he can still remember the laugh
2) killer comes back, shoots someone else, drives off laughing agains
i think 2 is very unlikely, doesnt make no sense, but thats what i thought initially
its prolly #2, a conversation, somethin like this:
banks father: what happened, i just heard some shots
banks: yea this guy drove by and started shootin, i still remember his laugh as he drove off...