Kurt was also an avid gun collector. Why would a man with every type of gun at his disposal choose a shotgun to kill himself with? You don't hole up in your loft with a shotgun to kill yourself, you do it because you think someone is trying to kill you, and Kurt supposedly stated to friends that he was afraid for his life.
Kurt had all his guns taken away from him after the sleeping pills and champagne overdose in Rome. He thought someone was out to get him, so he asked his friend Dylan Carlson of the band Earth to sell him one of his shotguns, and it was that same shotgun that ended Kurt's life.
I feel someone he TRUSTED came to see him, perhaps offering to give him a fix and let him crash...telling him they would "keep watch." They booted him up, he nodded out, and was murdered. I believe I know who the trusted "friend" was; they same guy who 2 weeks earlier went with him to buy the shotgun.