He has killed Rob Reiner and Danicka Patrick. In the same episode, he mowed through several spectators in the center of the track, caused other racers to crash (possibly die), and even ran a car into the wall, killing more spectators. You could also take into account the number of civilians The Coon ordered Cthulu to kill. He may have caused the deaths of Mr. and Mrs. Tenorman, but he didn't kill them himself. The rancher shot them because he thought they were trespassing. But he hasn't gotten away with all his crimes based on technicalities. He's been to a Juvenile Detention Center a few times. He went when he threw a brick at Token in "Cartman's Silly Hate Crime 2000" and when he tricked Butters into thinking a meteor hit the earth so he could go to Casa Bonita in "Casa Bonita". He even went to jail for locking hippies up in his basement in "Die Hippie, Die".
He gets away with because everyone in South Park are stupid and cowards and weak willed