Evidence is mounting that PSNI police agents were involved in the murder of a young Catholic man shot dead by unionist paramilitaries four years ago.
The parents of 19-year-old Gerard Lawlor have asked the Police Ombudsman Nuala O'Loan to investigate claims that the PSNI failed to arrest their son's killers in order to protect one or more informers.
The teenager had been due to move into a new home with his partner Siobhan and their 18-month-old son Josh days after he was shot dead by UDA gunmen in July 2002.
The PSNI later admitted it had not arrested or questioned anyone for the murder, despite police knowing the identity of the killers.
A PSNI detective claimed to have "no witnesses, no information", despite three witnesses coming forward to identify those involved.
The Lawlor family had originally believed that the PSNI were doing everything possible to apprehend their son's killers.
But over the last 18 months, the Lawlor family have become increasingly concerned that there was never any serious effort to catch their son's killers.
There were also concerns that PSNI patrols mysteriously withdrew from the area prior to the attack.
John and Sharon Lawlor and Gerard's partner Siobhan Ramsbottom have asked Mrs O'Loan to investigate serious failures in the PSNI murder inquiry.
One witness used the confidential police telephone line days after the murder to identify two unionist paramilitaries as having admitted to the murder several hours after the attack.
Neither of the named suspects was arrested.
After hearing nothing in the intervening four years, the same witness has come forward again this summer, offering to testify at trial.
The PSNI has claimed that it could find no record of the original telephone call made by X identifying the killers.
The Lawlor family have now learned that the PSNI have refused to investigate the claims in the absence of fresh corroborating evidence.
Last week John Lawlor said: "We trusted the police when they told us that they were doing everything they could to catch Gerard's killers...
"But now we believe the original police investigation was nothing more than a sham and that Gerard's killers were protected."
Gerard Lawlor's mother Sharon said the family hoped the ombudsman would uncover the facts.
"All we want is the truth. We want to know why there weren't more police patrols in the area, given that there had been a series of attacks earlier in the night," she said.
"We want to know why the police do not appear to have followed up on three different people's evidence about who may have been involved in Gerard's murder.
"Why does it appear that little or nothing was done to find these people?"
A spokesman for the Police Ombudsman's office confirmed it had been asked to investigate the PSNI inquiry.