Lyra McKee was a 29-year-old reporter who was killed in 2019 during riots in Derry. She was killed by a member of anti-peace process dissident republican group the New IRA.
The Police Service of Northern Ireland (PSNI) said the Hammerli X-Esse pistol they found last weekend was the gun that killed McKee.
They came to the conclusion after forensic tests on the weapon established it fired the rounds that killed the 29-year-old reporter during riots in Derry last year.
The PSNI said confirmation that the pistol was discovered during two days of searches over a site covering 38 acres in Derry.
The discovery marked “a significant moment in the investigation” into the New IRA killing.
READ MORE: Brexit U-turn: Government abandons plans for full UK border checks in major policy shakeup
Detective-Superintendent Jason Murphy, the senior investigation officer on the case, said the PSNI was pursuing the possibility that the gun had been stolen “some time ago”.
He added that several New IRA figures were responsible for getting the weapon on the night Lyra was killed.
Dt Supt Murphy said: “I know who they are and the public know who they are and I also know who the gunman is.
“For the New IRA the net is tightening.
“One positive result will have significant consequences for the New IRA.”
Det Supt Murphy added that a very detailed forensic examination was under way on the gun, ammunition and the plastic bags in which they were wrapped.
He said: “The gun jammed as the gunman fired and I know from the video footage that the gunman tried several times to eject the jammed rounds.
“For that reason, I have asked scientists to extend their forensic examination beyond the outside of the gun and forensically examine the inside mechanisms of it, to establish whether the gunman, in his haste to clear the blockage, may have left forensic traces inside the gun.
“We are using the most advanced DNA technology available and we will exhaust every opportunity to recover forensic evidence.”
Barnier blocks UK plans for secret Brexit negotiations [INSIGHT]
Frost send no-deal warning to EU [INSIGHT]
Michael Gove promises ‘under no circumstances’ will UK delay Brexit [LATEST]
He also claimed that he had the “unenviable task” of telling Ms McKee’s partner Sara and family that the gun had been recovered.
Murphy said: “For those with a conscience, Lyra’s murder will have played heavily on their minds every single day.
“As the net gradually tightens, those who fired the gun, transported it, moved it, stored it, carried it, hid it or interacted with it in any way, should expect the police at their door.”
The pistol was also discovered along with a fully primed bomb which the PSNI believe was planned to have been used to murder police officers.
Alongside the bomb, police found command wire for triggering bombs and a quantity of ammunition.
Paul McIntyre is currently being held in Maghaberry Prison facing charges for Ms McKee’s murder.
The 52 year old from Derry denies all charges, which include the murder, as well as possession of a firearm with intent to endanger life and professing to membership of a proscribed organisation.
A second man was also charged with offences relating to the rioting that preceded the shooting.