David Harker, 24, bragged to friends about his crime, but they did not believe him, a court was told.
Mrs Julie Paterson, 32, described by police as "vulnerable and child-like", went missing from her home in Darlington, County Durham, last April.
A murder hunt was launched after parts of her body were found a month later in a bin-liner hidden in a garden hedge.
The whole of the body was never recovered.
Police believe that she was strangled in Harker's Darlington flat.
Harker, 24, was due to stand trial at Teesside Crown Court when he admitted manslaughter on the grounds of diminished responsibility.
'Subhuman'
Superintendent Barry Peart, who led the investigation said after the case: "He has told over 25 people what he has done, but because of the grisly nature of what he was saying they did not believe him, they thought he was fantasising, but unfortunately he was not."
He said Harker, who has two tattoos across his temple saying "disorder" and "subhuman", killed the woman for pleasure.
Judge Mr Justice Bennett jailed Harker with a recommendation that he serve at least 14 years before any parole is considered.
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