Convicted child killer Robert Howard was responsible for the death of Co Tyrone schoolgirl Arlene Arkinson, who went missing in August 1994 after a night out in Donegal, a coroner has found on the balance of probability.
Howard, originally from Co Laois, was charged with the murder of Arlene Arkinson in 2002 but acquitted in 2005.
He died in prison custody in England in 2015 while serving a life sentence for the rape and murder of 14-year-old Hanna Williams from London.
Arlene's body has never been found despite extensive searches.
Following a long-running inquest at Omagh courthouse, coroner Brian Sherrard found that she died on the morning of Sunday August 14 1994.
"There is no record of her being alive after that date," he said.
"Robert Howard - a violent sexual offender and the last person to be seen with Arlene, in the early hours of August 14 1994 - was responsible for her death."
Arlene (15), from the village of Castlederg in Co Tyrone, disappeared in August 1994 following a night out at a disco at Bundoran in Co Donegal.
She was last seen in a car driven by prime suspect Howard.
Reacting to the coroner's ruling, Arlene Arkinson's sister Kathleen said there was now no doubt Robert Howard murdered her.
Ms Arkinson, who also alleged that that Howard had been working as a state agent, called for a public inquiry into the convicted killer's activities in Northern Ireland.
"This was a 14-year-old inquest, nearly as long as Arlene's life," she said.
"An inquest that Howard and the state never wanted. It was opened in November 2007, and only finishes today.
"Twenty-seven years on from Arlene's murder, I am still searching for her body. What else can I do? What else would anyone expect me to do? Despite what has happened, I have placed my faith in our justice system and went with it.
"Therefore I appeal to the justice minister (Naomi Long) to examine Arlene's case carefully.
"When she does, she will see that the need for a public inquiry into the activities of Robert Howard in this jurisdiction and his status as an agent for the RUC, which has led to death and misery for many people, will be unavoidable.
"I guarantee the minister that the more she looks into Arlene's case, the more outraged and terrified she will be on behalf of the public. But, above all, I want a Christian burial for my sister. In seeking the truth, through public inquiry, maybe I will achieve that."
rkinson family solicitor Des Doherty said he also suspected Howard was a police agent.
"He had to be working for the police, how else could he have got away with such murder?" he said outside Omagh courthouse.
Mr Doherty questioned the state's move during the inquest process to exempt some evidence by seeking public interest immunity (PII) certification.
"What was all that about, what was going on there, who or what were they protecting?" he said.
Asked if he believed Howard was allowed to get away with murder, Mr Doherty said: "Well that's what the family are saying, and I support the family fully in that view. What other conclusion can you come to, because he did get away with murder?"
He said a public inquiry would be able to compel all the surviving former police officers involved in the case to give evidence about what they knew about Howard.
The inquest into Arlene’s death finished hearing evidence in 2019, after more than a decade of stop-start hearings.
Despite extensive searches, Arlene’s remains have never been found.
A grave in Co Sligo was exhumed by gardaí in March 2018 but was found to contain the remains of an adult male.
Arlene’s family have repeatedly said that they will never give up hope of recovering her body.
The inquest first opened in November 2007 but has faced several delays over the years due to a number of factors including legal challenges, resource issues and difficulties obtaining documents from gardaí.