To the outside world, Dennis Nilsen was a quiet civil servant who kept himself to himself.

But behind closed doors, the Scot hid a dark, twisted secret which led him to become one of Britain's most infamous serial killers.

Nilsen, also known as the Muswell Hill Murderer, was luring young, vulnerable men to his north London home and killing them in a murderous spree of near-unparalleled savagery.

The 72-year-old, who died in prison on Saturday, is believed to have killed as many as 15 young men, most of them homeless homosexuals, in the 1970s and 1980s.

READ MORE: Neighbour's observation ended Dennis Nilsen's murderous spree

After strangling or drowning the men, the killer would often live with their corpses for days, bathing and dressing them, placing them around his home and performing sex acts with them before eventually dismembering the bodies.

His warped crimes were only detected by chance when a drain outside his home in Cranley Gardens, Muswell Hill, became blocked.

When workmen investigated, they discovered human remains and Nilsen's killing spree was finally discovered.

He was jailed for life in 1983 on six counts of murder and two of attempted murder.

Nilsen, who grew up in Fraserburgh, Aberdeenshire, spent 12 years with the army and a brief spell in the Metropolitan Police before finally securing work with a job centre, where he also served as a shop steward.

He began killing in 1978 to stop himself from feeling lonely after a split with a boyfriend.

After picking up a young man in a pub who stayed the night with him at his then house in Melrose Avenue, he realised in the morning that his companion would leave so calmly strangled him with a tie.

READ MORE: Neighbour's observation ended Dennis Nilsen's murderous spree

That night he slept with the body and then hid it under the floorboards for seven months before eventually burning the corpse in his garden.

That young man was Stephen Holmes, a 14-year-old boy.

Others soon followed - Martyn Duffey, Billy Sutherland, Douglas Stewart, Malcolm Barlow and several men he could not name.

But the stench of the corpses was beginning to cause a problem and neighbours began to complain, so Nilsen moved to the flat in Cranley Gardens.

There he killed another three men - John Howlett, Graham Allan and fellow Scot Stephen Sinclair, from Perth. He again lived with their bodies and defiled them before cutting them up.

Because he had no garden at the flat, he could not burn their bodies so began boiling body parts to remove the flesh and stuffed the rotting parts down the drains.

When detectives first searched his flat after the plumbing discovery, they were met with the horrid stench of decay as some of the remains were still under his floorboards and in cupboards.

In a grim interview in 1993, Nilsen described how he liked to dress the bodies in Y-Fronts and a vest, then undress them.

He added: "The most exciting part of the little conundrum was when I lifted the body and carried it.

"It was an expression of my power to lift and carry him and have control.

"The dangling elements of his limp limbs was an expression of his passivity. The more passive he could be, the more powerful I was."

READ MORE: Neighbour's observation ended Dennis Nilsen's murderous spree

The killer also provided horrific detail on how he dealt with the bodies, saying he was physically sick after cutting the innards from some of his victims to tackle "the smell problem".

In the final section of the interview, Nilsen said: "The bodies are all gone. Everything's gone, there's nothing left. But I still feel spiritual communion with these people."

A spokesman for the Prison Service confirmed Nilsen's death on Saturday.

A statement read: "Dennis Andrew Nilsen, date of birth November 23 1945, died in custody at HMP Full Sutton on Saturday, May 12 2018.

"As with all deaths in custody, there will be an independent investigation by the Prisons and Probation Ombudsman."