Jason Conroy, 19, strangled Melissa Mathieson, 18, at Alexandra House, Bristol, and planned to drag her body back to his room and sexually abuse her

A teenager has been jailed for life for the murder of an 18-year-old woman in a residential home supporting people with autistic spectrum disorder, hours after she told staff he was stalking her.

Jason Conroy, 19, strangled fellow resident Melissa Mathieson at Alexandra House in Bristol and planned to drag her body back to his room and sexually abuse her.

It has emerged that Conroy had a fascination with necrophilia, once trying to strangle a teacher so he could abuse her. He also attempted to kill his mother by putting a duvet over her head for the same reason.

Facebook Twitter Pinterest Jason Conroy had a fascination with necrophilia, the court heard. Photograph: Avon and Somerset police/PA

Sentencing Conroy at Bristol crown court on Friday, Judge Graham Cottle told him he would have to serve at least 19 years’ imprisonment before he could be considered for parole.

The judge said the murder was clearly sexually motivated, adding that Conroy had exhibited “sexual deviancy of the most worrying kind”.

Cottle said: “You developed a fantasy of having sex with a woman who you strangled first, at least to the point of unconsciousness if not death. While at Alexandra House you had become fixated with Melissa. You stalked her and your intention was to have sexual intercourse with her.

“You knew she would not consent to it and so you determined to kill her and then have sex with her. The conclusion that I reach is that you pose a very serious danger to the public, in particular young women, and the fixing of the minimum term should properly reflect that finding.”

Mathieson’s family has expressed deep concern that Conroy had been placed in the home despite his history of sexual deviancy. In a statement they said: “Melissa believed wholeheartedly that the care system was the safest place to be to help her with her difficulties.

“We feel that there are still many questions that need to be answered by many organisations, including social services and the NHS, about how Melissa and Jason Conroy came to be in a situation which ultimately led to Melissa’s death.”

Paying tribute to the 18-year-old, they said: “Melissa’s death has left such a huge, huge hole in our lives. She always brought a bit of a challenge in all our lives, and things were quiet without her when she stayed at different places during her last 10 months.

“We keep thinking we are going to see her bound through the doors. But now that she is not here at all – it’s the emptiness that is overwhelming. Melissa did not have a nasty bone in her body; she was a gentle, kind and lovely girl.

“We know better than most people the difficulties that autism can present so our feelings about Jason Conroy are not based on ignorance of his condition. What he has done is awful; we cannot comprehend it.

“It has been incredibly difficult to sit through the trial and listen to the evidence, especially the history of Jason Conroy’s previous sexually deviant and aggressive behaviour.”

A safeguarding adults review is under way. Senior investigating officer Andrew Mott, of Avon and Somerset police, said: “This was a desperately sad case in which a young person’s life was cut tragically short.”

The review will look at why Conroy was not subject to greater supervision at Alexandra House, which looks after up to 14 people aged 18-50 with autistic spectrum disorder and Asperger syndrome.