- Video report by ITV News Correspondent Peter Smith
The man leading the hunt for the killer of journalist Lyra McKee has spoken about a "new breed" of terrorist stalking the streets of Northern Ireland.
Detective Superintendent Jason Murphy, of the Police Service of Northern Ireland, said terrorists were lurking in the shadows.
Appealing for more help from the community in Londonderry, Det Supt Murphy said: "My broader concern is that what we are seeing is a new breed of terrorist coming through the ranks and that for me is a very worrying situation."
He confirmed that two men, aged 18 and 19, arrested in connection to the murder of Ms McKee were being held under the Terrorism Act.
The men have been taken to the Musgrave Serious Crime Suite.
He told a press conference he believed the two were members of the New IRA.
Ms McKee, 29, was hit by a bullet as she watched the rioting in the Creggan area of Londonderry, on Thursday night.
Det Supt Murphy said: "The brutal nature of that attack has sent shockwaves around the world.
"The gunman showed no thought for who may have been killed or injured when he fired those shots.
"The individuals responsible for Lyra's murder continue to hide in the shadows.
"They attempt to justify their actions to each other. They have shown no courage to offer any explanation directly to Lyra's family."
He said there has been a sea-change in community attitudes towards the gunmen, demonstrated in the revulsion expressed by many at Miss McKee's killing.
The New IRA is an amalgam of armed groups opposed to the peace process and it recently claimed responsibility for parcel bombs sent to London and Glasgow in March.
Mr Murphy conceded there remains fear of reprisals for giving information to police from the shadowy gunmen.
He said: "Individuals continue to exert influence over communities, not just in the Creggan but in other parts of the communities as well.
"This intimidation and fear creates a real concern for local residents to come and talk to us as police officers."
The PSNI released footage on Friday evening of the moments leading up to Ms McKee's death.
In the grainy footage, a hooded gunman can be seen peering round a building before taking aim and firing.
In other images on the video, Ms McKee is identified in the crowd watching the late night disturbances in the Creggan area of Londonderry on Thursday.
She is seen to get her mobile phone, stand on tip-toes and take a picture above the heads of the people in front of her.
As the footage moves on, the masked figure of the gunman is spotted front on lurking by the corner of a building.
Ms McKee was standing near a police vehicle and was fatally wounded, hit in the head.
She was taken to hospital by officers but later died.
CCTV footage also shows an individual picking up something from the ground on the same corner - possibly shell casings from the firearm.
There is no suggestion the men arrested are seen in the video released by the PSNI.
Addressing Ms McKee's suspected killers, Deputy Chief Constable Stephen Martin told a press conference in Londonderry on Friday afternoon: "This was not done to further any cause – this will have achieved nothing other than to plunge a family into grief."