What happened to the lead singer in nirvana?

well the note they found said he didnt want his daughter to end up like him but i don't believe he killed himself i think he was murdered but what ever that's what the note said. listen to the song Mrs.Buttersworth. It is one of there early songs and it is on their CD Sliver: The Best Of The Box. The first Words say it all... I know he got famous but these feelings stuck with him.