The twisted 24-year-old had an unnatural obsession with deviant sex and confessed in a letter to his mother that the 17-year-old had been strangled during violent love making hours after they met for the first time following his release from jail just three days earlier.
Foster, whose two pleas to let him strangle a previous girlfriend during sex had been rejected, wrote: "We ended up having sex together. She tells me she likes to be strangled so I obliged. I strangled her and she loved it so much....but then as I released her, her eyes closed."
He has been jailed for life for murdering Megan with a minimum term of 26 years.
But he repeatedly refused to tell police or prosecutors exactly how Megan met her death in his room at the New Horizons hostel for ex offenders in Highgate Road, Brierley Hill on April 16, Easter Sunday, last year - and declined to give evidence during his Wolverhampton Crown Court trial.
Foster hid the body in a wardrobe that was deliberately wrapped in cling film to speed decomposition of the corpse. The state it was in when found almost three weeks later on May 4 made it impossible to pin point the exact cause of death.
Watch the last time Megan was seen alive:
A shirt of his with Megan's blood on it was found in a dustbin. It was twisted and torn in a way that suggested it could have been used as a ligature. Interrogation of his two phones showed he made numerous internet searches for 'snuff' videos after the death.
He was arrested later the same day as the body was found and admitted preventing her lawful burial but denied manslaughter and murder.
Det Insp Caroline Corfield, who led the investigation, said: "He never showed any remorse for Megan's death.
"In hiding the body his only concern was himself and he almost evaded justice by deliberately causing her body to decompose quickly by wrapping the wardrobe in cling-film.
This made it impossible to give a precise cause of death and added to the distress of her family."
The D.I added: "The letter we found contained half the truth but he has consistently covered up what really happened. This was a terribly tragic death of a teenager with her whole life in front of her.
"Despite Megan’s apparent independence she was a vulnerable young lady who would never have imagined the dangerous lair she was walking into when she entered Foster’s room.
"He had an unnatural obsession with deviant sexual activity and he disposed of Megan’s young life to satisfy his own twisted desires. For Megan’s family, hearing the details of this evidence must have been unbearable.
"I am pleased the jury saw through his thin fabric of lies and found him guilty of murder causing Megan's death and I can only hope this gives her family some sense of justice."
Watch DI Corfield discuss the case:
Judge James Burbidge QC said while sentencing Foster to serve at least 26 years behind bars before being considered for parole: "Megan had an immediately trusting character which was entirely misplaced as far as you are concerned.
"She took a liking to you and agreed to have sex but did not agree to be strangled by you.
"She had become more sexually active but that does not begin to suggest that she agreed to auto erotic asphyxia.
"You asphyxiated her and, instead of reacting in a compassionate and decent fashion, you did not ring for an ambulance but bundled her body into a wardrobe.
"You have chosen not to tell the truth at any stage. You are a liar who tries to serve yourself in what you say. She trusted you throughout the sex and you strangled her. She did not agree to it.
"I am sure you carried out your fantasy to satisfy your perverted sexual pleasure.
"You sought to engage in some warped and dangerous activity. I fear your future conduct to women."
The judge paid tribute to the dignified way in which Megan's family, her parents Dawn and Martin Bills and her brother James, had conducted themselves throughout the sometimes harrowing trial.