No, I’m sorry. This is the serial killer who murdered your father lying unconscious in front of you. You’ve shown you’re willing to kill him in warm blood (as evidenced by trying to shoot a “helpless” guy tied to a chair). You know he’s a menace that’s been pretty much impossible to stop. So, now that he’s helpless and unconscious in front of you, you’re going to take the corpse of a virtual stranger and carry it (via taxi - you think would make it hard kind of hard to flag one down with a corpse in your arms) to his mother?
Really, it’s not like Peter is going to get more dead while you find your gun and kill Sylar or, if necessary, smash his brains out with a lamp.
Mohinder, anyone else that dies due to Sylar is on your head.
So, I was looking for a REASON, not a recounting of the chain of events - I got that already from watching it.
Being scared as fuck. I mean, he already tried to shoot him, drugged him and everything. Short of pulling a Highlander on him, what could he do? Also, perhaps he already thought he’d killed him. I mean, the guy didn’t have Claire-power yet, and being slammed with a bulletin board in real life would probably cause some serious head trauma. Further, of course, you don’t want to kill off the main villain in the middle of the season. I suppose Mohinder’s character motivation is supposed to be fear for Peter, fear of Sylar and wating to GTFO, but as a plot scene it is weak.
I don’t think it’s ever been stated explicitly what he does with the brains. Personally, I don’t believe he has to kill people, I think he just thinks he does. And as has been said, he’s batshit crazy.