A care worker has been found guilty of the "execution-style" murder and rape of 13-year-old Lucy McHugh who was stabbed to death in woodland in Southampton.
Stephen Nicholson, 25, showed no emotion as he was convicted at Winchester Crown Court of her murder as well as three counts of rape when she was aged 12.
The murder investigation was hampered when Nicholson refused to reveal his Facebook password and police had to wait months before the social media giant handed over details of communications between him and Lucy.
This prompted calls from senior police and politicians for detectives to be given quicker access to social media accounts when investigating serious crimes.
A probe has also been launched into the handling of the case by social services after two schools alerted them that Lucy had told teachers she had been in a relationship with the defendant.
After the verdict, Lucy's mother Stacey White, 31, thanked friends and family and police who helped bring the killer to justice.
In an emotional statement following the welcomed verdict, she said: 'I would like to thank from the bottom of my heart our close family and friends for their support during this harrowing time.
'The dedication of Hampshire Constabulary, the specialist teams across the country and the local community helped get justice for my precious daughter Lucy.'
Lucy was lured by Nicholson to woodland at the outdoor Southampton Sports Centre on July 25 last year where he stabbed her 27 times in the neck and upper chest.
Nicholson has been described by police as a "predatory paedophile" who had abused the "vulnerable" youngster for more than a year while living as a lodger at her family home.
He then killed her to silence her when she threatened to reveal their sexual relationship.
She had also said that she would tell her mother that Nicholson had got her pregnant, although a post-mortem examination showed that she was not pregnant at the time of her death.
Nicholson is understood to have been living with the family in the months before the teen's death and was a colleague of Lucy's mother, Stacey White, a careworker, as well as a part-time tattooist.
The trial heard that Nicholson, described by police as a "predatory paedophile", had abused Lucy for more than a year while living as a lodger at her family home.
William Mousley QC, prosecuting, described the murder as premeditated and a "execution-style" killing.
Detective Superintendent Paul Barton, of Hampshire police, said after the trial: "I would describe Nicholson as cold and calculated, I would describe him as a paedophile and I think he is someone who only thinks about himself and has taken full advantage of this family that have looked after him, provided a roof over his head.
"He has targeted Lucy, taken advantage of her and when she wanted a relationship with him, he has taken the decision to silence her once and for all by brutally killing her."
The investigation into Lucy's death, described by the CPS as "one of the largest in criminal history", was obstructed when Nicholson refused to give police his Facebook password - for which he was previously jailed for 14 months.
After applying through the US courts for access to his account, prosecutors only received a log of his Facebook contacts with Lucy, but not the content of any messages.
It finally arrived the day that the trial started.
The defendant, who admitted dealing cannabis, claimed he had not wanted to reveal his drug contacts via his Facebook account out of fear they would attack his family.
Nicholson, a tattoo artist, was convicted of targeting another girl aged 14 who he had sex with as a trade for giving her a cheaper tattoo.
The defendant denied having an appetite for sex with underage girls and said he did not have a relationship with Lucy.
He claimed Lucy had been "stalkerish" towards him and he had been at the home of an elderly friend when she was murdered.
Nicholson was linked to the murder through DNA evidence from both him and Lucy found on clothing, described by prosecutors as his "murder kit", which was discarded in woodland in Tanner's Brook, about a mile from the murder scene.
He also tried to cover his tracks by inflicting wounds on Lucy that could be interpreted as self-inflicted and also posed in different clothing on CCTV at a Tesco Express store.
The court heard that Nicholson, a father-of-one, had a love for reptiles and had a collection which included 12 pythons, chameleons, geckos and corn snakes.
Nicholson also told how he enjoyed "soft choking" women during sex which involved squeezing their neck to intensify the sexual effect.
Nicholson, 25, of no fixed abode, denied the charges but was found guilty on Thursday at Winchester Crown Court.