There's a lot of details I'll miss, but the short of it is the documentary is told by a private investigator that Courtney Love hired to find Kurt when he was "missing" and a couple of investigative journalists. The P.I. was a veteran detective for a police department (can't remember if it was LAPD....in any case they had a few people on stating how exemplary this guy's record was while he was on the force) and thought the whole thing was fishy from the get go and actually ended up continuing to investigate the death on his own even after Kurt was found/ruled a suicide.
They don't get into at all who they think killed him...they just don't really think it was a suicide. The P.I. actually recorded every conversation he had with Love after their first meeting due to how shady she seemed and showed that a lot of what what the media was reporting was false information (imagine that) and much of it was spoon fed from her. They were going to get a divorce and he had gotten a prenup meaning she would be getting a small settlement. Since he died before the divorce, she ended up inheriting up to a billion dollars of his net worth in royalties. None of his close friends or people that really knew him say he was suicidal and one of their close friends who happened to be an attorney for the both of them is on tape with the P.I. saying she thought the whole suicide thing was garbage.
They've had independent people analyze the suicide and the last little bit of it is written as a typical suicide note (to the point where the professionals think it was almost over done) while the major portion of it is completely different and they said it actually looks like somebody could have copied his handwriting.
The theory was he shot up and then used the shotgun upside down and his thumb to pull the trigger. His death grip on the barrel of the shotgun goes along with that, except the ejection port of the gun is in the complete opposite direction of where the shell was found, which is pretty much impossible. Also the amount of heroin they found in him was multiple times the fatal dose meaning there was pretty much no way he was conscious enough to handle the shotgun well enough to kill himself with it (not to mention it pretty much never happens that suicidal people shoot up enough to kill themselves and then also use a gun).
And of course the police work was pretty much garbage and there's all kinds of evidence and toxicology reports that still haven't seen the light of day.
. My daughter met her and Stevie Nicks at that time..