3)  Rear End PGH at the beginning.
I'm not sure what this accomplished.  The scene describes multiple impacts.  Possible results I can identify are:

• Murph getting called in on the case early
• Delay's Harry's being able to get onto the case
• Makes Harry miserable early.

This seemed like an act of opportunity and desperation.  It was violent and not very precise.  The main reason why I pin TTH for this is because if he was indeed around he would probably have the opportunity, and maybe need the above 2 things accomplished, and also because I remember being lead to believe that we would get resolution to this mystery and seeing the scene from TTH's perspective ramming PGH would certainly give us closure. (the last is red because I'm not happy that I don't know where that memory comes from)

I always liked TTH for being the one to rear end PGH because if PGH hadn't been in his fender bender then he wouldn't have been all hazy, he would have unplugged his phone and Molly wouldnt have contacted him in time, So he would have tried using LC and blown up and died. I like TTH for tying up PGH just long enough to get caught up in the Molly Case, and giving TTH the chance to fix LC which he could do because he was the one who made it in the first place.