The gunman who murdered journalist Lyra McKee may have left vital DNA clues on the weapon when he was clearing jammed rounds.
A handgun, recovered in a search of 38 acres of land in Derry city last weekend, has now been identified as the weapon used to murder the 29-year-old.
Ms McKee was covering clashes between police and dissident republicans in the Creggan part of the city when she was shot dead in April last year.
Det Supt Jason Murphy, of the PSNI serious crime branch, said last night the gun jammed as it was being fired and video footage showed 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," said Det Supt Murphy.
"We are using the most advanced DNA technology available and we will exhaust every opportunity to recover forensic evidence".
He said that work would take some considerable time to complete, particularly because of the intricate examination of the internal mechanisms.
Det Supt Murphy said police already knew who was involved, including the identity of the gunman, and he had asked the scientists to find him the evidence that would enable him to complete the jigsaw of events that he had been building since the night Ms McKee was murdered.
Forensic tests have been going on all week to establish if the gun - identified as a Hemmerli X-Esse pistol - was the weapon used.
A detailed examination of the ammunition and the plastic bags in which they were wrapped is ongoing.
Since April 18 last year, Det Supt Murphy said, they had been focused on seeking to bring to justice those involved in the murder.
"I am as clear today as I have ever been that the bringing of that gun on to the streets involved a number of senior figures in the New IRA," he added.
"Today's confirmation opens up a new avenue of investigation for my team.
"We will be relentless in pursuing opportunities to bring to justice every person who was involved in the chain of events."
He said the gun was fired intentionally towards police Land Rovers, placing many officers at risk.
"The presence of bystanders like Lyra, who were watching the unfolding events, was an inconvenience to the terrorists but the gunman clearly placed no importance on that," he said.
"Any reasonable assessment must be that for the New IRA, the community were, and continue to be, expendable collateral damage.
"Lyra's murder was not an accident - it was an inevitable and entirely predictable result of terrorist violence."
The police investigation also extends to finding the person responsible for the disappearance of the weapon and who transported it to the site where it was found, along with a fully primed bomb, near the back gardens of a housing estate and close to a children's play den.
"The disregard shown by the New IRA is staggering but completely unsurprising. They continue to put their own agenda above the rights of local communities to live in peace," said Det Supt Murphy.
"One positive forensic result, coupled with the extensive evidence we have already gathered, will have significant consequences for the New IRA."