Police in Northern Ireland have found the gun that killed journalist Lyra McKee in Derry last year.
The officer leading the murder investigation says he knows the identity of the gunman and believes he may have left forensic evidence on the weapon.
The German-made Hammerli X-esse handgun was found during police searches in Derry at the weekend.
The PSNI has said video footage of the shooting shows the gun jamming after two shots were fired, and the gunman unjamming it before firing further shots.
The weapon was used in a number of previous shooting incidents by the dissident republican group referred to as the New IRA.
"For us, investigatively, this is incredibly important," said Detective Superintendent Jason Murphy.
"There's an interaction that takes place between the gunman and the gun, which seeks to block it. It is that interaction that I think may be important to me, and the potential the gunman may have inadvertently left DNA or fingerprints on the inside of the gun, as opposed to the outside surfaces.
"The moving parts of a gun are extremely fast, often very sharp. The outside edges can be fairly flat, quite easy to wipe down, so I'm less concerned about the outside surfaces and more concerned about the inside surfaces.
"I believe there's a potential here for the gunman to have inadvertently left DNA or fingerprints on the inside mechanisms of the weapon.
"The work that's currently ongoing is a very detailed forensic investigation both inside and outside of the gun to forensically link the gunman and the New IRA to the murder of Lyra McKee."
Det Supt Murphy said he is confident he knows the identities of all those involved in the incident in the Creggan area of Derry in April 2019, when shots were fired at police officers.
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Ms McKee was one a number of civilians standing close to a Land Rover observing rioting when she was shot in the head.
Det Supt Murphy said the person who fired the fatal shot is still living in Derry.
"I know where the gunman is and i know who the gunman is, and I know an awful lot about his associates and, more importantly for Lyra's family, I understand the role that each and everyone of those individuals played on the night.
"I described to the family on day one of this investigation that it was a thousand piece jigsaw. I've now been able to put into place a significant number of those pieces in that jigsaw to be able to tell the family the story and show them the pictures.
"This forensic examination of the gun I hope will enable me to put the last few pieces of the jigsaw into place and enable me to bring people to justice for the murder of Lyra McKee."
The officer briefed Ms McKee's family and partner on the development yesterday.
"They are very keen for me to emphasise to the public that they are relieved that nobody else will live through the turmoil they've lived through as a result of the use of that gun in the future," he said.
