Corrupt and inefficient law enforcement + coroner practicing the autopsy
For Seattle PD it was a slam dunk case when it shouldn't have been, same with Chris Cornell, declared as SUICIDE in less than 24 hours and without the medical/chemical results to back it up.
Once the inconsistencies began to be made public (mainly during Nick Broomfield's documentary "Kurt and Courtney" in 1997) the case had been closed for 3 years, and people don't know this but Seattle PD would have been sued and torched if they backtracked because of the immense amount of copycat suicides of kids losing hope cause their idol did. It's very sad.
The documentary I posted clears all that... murdering a drug addict grunge rock star who sings about being depressed and disenfranchised and staging it as suicide is one of the easiest crimes. It's expected and it added to the folklore. Sadly, for the worst.
That said since Kurt was leaving Nirvana and Courtney, is not that farfetched to think Courtney had David Geffen's blessing to off Kurt, for monetary AND PAYBACK REASONS:
For the most part, the band kept censorship of the cover at bay. Some reports say Cobain insisted any censorship be accompanied by the following message: “If you’re offended by this, you must be a closet pedophile.”
This was his reply when David Geffen (CEO of GEFFEN records, who is a rumored rapist pedophile and human trafficker) wanted to boycott Kurt's chosen picture for the Nevermind cover. Geffen was involved in the murder of Michael Jackson and Chris Cornell as well. It is well known Geffen is one of the heads of the so-called Velvet or "Gay" mafia that runs Hollywood... he is involved in much shady stuff and has no qualms about getting people offed... just like Tom King, the writer of his autobiography. Geffen is worth $7.8 BILLION... he can grease and buy almost anyone... Kurt WAS WORTH MORE DEAD, THAN LEAVING NIRVANA AND BEING ALIVE. His suicide propelled him into legendary status and the number of records sold was unbelievable.