For some reason I felt bad for Dolan being buried alive in the Caddy at the end of the film. It was like watching Poe's 'The Cask of Amontillado TV/film production where John Heard buries that guy alive in a wall. Robinson should have maybe tied him up or held him at gunpoint and call the police up to say he caught him so he would go to jail. I felt Robinson took it a little too far and went all psycho. I guess revenge turns some people into psychopaths.
Well thats kinda the point of the story/movie, a normals guy's descent into madness to get revenge. Also he knew if he went to trial theres a chance he could get off as rich people tend to do.
As for sympathy, I think the filmmakers figured that might happen despite the fact that he's a murderer and sex trafficker.. so they made a point to show that Dolan was on his way to get involved in some child trafficking business before the end, to make sure you weren't gonna feel too sympathetic towards him.
They made a point to say that some of the women they found buried had been buried alive. That was supposed to make people less sympathetic. It worked for me, anyway.