What and when did Kenny waters die?

Answer 1

Kenny waters died on Sep 6, 2001. He died of a freak fall, he was climbing over a 15-foot wall after having dinner in his brothers house, withSuch a shame he spent 18 years of his life in prison and he dies 6months after he was released in March 2001.

Answer 2

The Bastards.

When Stan says "Oh my god! They killed Kenny!", He is referring to Matt and Trey themselves.