Sean O’ Donnell – Media Relations Officer for the Seattle Police Department - In response to why no legible fingerprints were found on the shotgun - "I think its clear that anyone who is familiar with firearms and there use would know that as they hold a weapon that frequently that weapon will move in their hand. Additionally when that weapon is discharged that causes a jerking motion which causes the hands to move over the surface of the weapon. And all of those factors could cause any fingerprints that may have been left on the weapon to be unusable."(Unsolved Mysteries)

Tom Grant - "I would agree...if the shotgun had never been touched until the moment it was fired into Cobain's mouth."

Above is an excerpt taken from the crime scene evidence log. Both the shotgun and nylon shotgun case are booked under one item; the shotgun was transported in its case - wrong procedure.
Not only that but the request to have the firearm fingerprinted wasn't submitted until one month after the incident.