Unemployed John Maden, 38, lured 12-year-old Tia Rigg to his home on the pretext of her babysitting for the father-of-one.
But Maden, who hoarded extreme internet porn depicting the abduction, sexual torture, rape and killing of children, drugged and bound his unsuspecting niece before acting out his sick fantasies.
Tia, the daughter of Maden’s sister, Lynne Rigg, was subjected to horrifying sexual injuries with a broom handle before being stabbed and strangled with a guitar wire.
Maden, separated from his wife, had studied a Snuffing Handbook and looked up how to drug youngsters to prevent victims going into clinical shock and unconsciousness to prolong their agony as they are tortured and killed, the court heard.
Lynne Rigg and other members of her family sat head bowed, covering their faces with their hands and weeping silently as details of Tia’s last moments were read to the court.
The defendant had been due to go on trial but instead pleaded guilty to murdering Tia at his home on Dalmain Close, Cheetham Hill, Manchester, on April 3.
Mr Justice Keith said the case was horrific and truly exceptional and a mandatory life sentence for murder must mean he will never be released.