I suppose it was inevitable that Gabriel Knight would either be a H or a villain. So he's a H. I spent a good deal of the book trying to place the bit with his late fiancee though. Was her demise in a previous installment? Dunno. Would have to dig out the series to find out.
Anyway... a guy is killed. And...many things come to light, including a bit more thorough investigation into the death of the fiancee. Odd really, that the previous investigation never noticed things the h conveniently noticed.
The scapegoat was an idiot though. Really too obvious. Also, since when does an addict have a hotrodded muscle car? Seems more likely he'd sell it for a fix the first chance he got. Not to mention, things like J.O.B.s and money are required to pay for such things.
There was a bit of humor in that the h called Knight a caveman. He took it well, considering.