RUC officers were not complicit in the murder of a colleague at a Belfast ice cream parlour, the Police Ombudsman has said.

Constable John Larmour was shot dead by the IRA in October 1988 at the shop on the Lisburn Road and no-one has ever been prosecuted.

Members of the officer’s family made allegations implicating Special Branch officers and police informants in the killing.

They drew links with a series of other murders and terrorist incidents over a 17-year period.

Ombudsman Dr Michael Maguire said: “We found no evidence to suggest that Special Branch, or any other element within the RUC, aided, abetted, counselled or procured John Larmour’s murder, nor that they could have prevented it.

“Similarly, we found no evidence to support allegations that police failed to charge suspects in the murder or that they protected IRA members from being brought to justice.”

Investigators interviewed more than 40 witnesses, including retired police officers, considered case papers and forensic files and examined intelligence held by police.

They established that one of the weapons used to kill Constable Larmour was likely to have been originally owned by the RUC.

Dr Maguire said PSNI records did not show to whom it was issued and were unable to establish if it was ever lost or stolen.

Many of the allegations were underpinned by a belief that there was a fraught relationship between Special Branch and Constable Larmour and as a consequence some of its officers became complicit in his murder, the watchdog’s office explained.

The ombudsman investigation found evidence of a fractious relationship but said the evidence did not support an allegation that a charge of perverting the course of justice made against Constable Larmour was initiated by police to force him from the force.

The ombudsman also did not substantiate an allegation that Constable Larmour intervened to stop a robbery being carried out by police informants, who officers then sought to protect from justice.