Two teenagers have been arrested under the terrorism act in connection with the murder of journalist Lyra McKee, police have said.
The men, aged 18 and 19, were held by detectives from the Police Service of Northern Ireland's major investigation team and taken to a police station in Belfast for questioning.
Ms McKee, 29, was shot in the head as she covered disturbances on the Creggan estate in Derry on Thursday night and died later in hospital.
The PSNI, which released CCTV of the incident in the hope it would help identify the killer, said a gunman fired shots towards police officers at about 10pm.
In her final moments, Ms McKee is seen standing among a crowd of other innocent bystanders and raised her phone in the air, apparently to photograph the violence.
In shaky mobile phone footage also released by detectives, a masked attacker leans from behind cover and appears to shoot towards police and onlookers.
Trouble began as officers carried out a search operation aimed at disrupting dissident republicans ahead of this weekend's commemoration of Irish independence.
Officers say around 50 petrol bombs were thrown in the confrontation and two cars were burned out.
Ms McKee, who had tweeted about the "absolute madness" in the area in the hours before she lost her life, was standing near a police 4x4 vehicle when she was hit.
In the video, a figure near the gunman appears to crouch and pick something up from the spot where the shots were fired, seemingly confirming detectives' theory that more than one person was involved.
On Friday evening, Ms McKee's partner Sara Canning told a vigil in Londonderry: "Our hopes and dreams and all of her amazing potential was snuffed out by this single barbaric act.
"It has left me without the love of my life, the woman I was planning to grow old with."
Detectives have said the New IRA, a dissident republican group, was most likely behind the reporter's killing.
Saoradh, a political party with links to dissident militants, released a statement claiming a "Republican volunteer" shot Ms McKee while attempting to "defend people" from the PSNI.
The force's Assistant Chief Constable Mark Hamilton called the killing a "horrendous act", carried out by people that "do not care who they harm".
Detective Superintendent Jason Murphy, who is leading the inquiry, described the murder as "senseless and appalling beyond belief".
Prime Minister Theresa May and Taoiseach Leo Varadkar condemned the killing, while former US president Bill Clinton tweeted: "Heartbroken by the murder of Lyra McKee and the violence in Derry."