Journalist Lyra McKee was shot in the head late Thursday as she watched the unfolding drama in the streets around the Creggan estate in Derry.
The rioting that led to McKee's killing began after police carried out searches for weapons and ammunition.
A gunman fired shots at police officers and the journalist, who was standing near a police 4x4 vehicle, was wounded. She died later in hospital.
Earlier, the Belfast-born McKee, had posted an image from the riots, accompanied by the words "Derry tonight. Absolute madness".
Some officials blamed Thursday's unrest on the "New IRA", a republican paramilitary group opposed to the shift towards non-violent tactics to bring about a united Ireland.
The New IRA (Irish Republican Army) is an amalgam of armed groups violently opposed to Northern Ireland's peace process. It claimed responsibility for parcel bombs sent to London and Glasgow in March.
Increased tensions with Brexit
There have been concerns that paramilitaries could be seeking to exploit the current political turbulence over Northern Ireland and its border with the Republic of Ireland, caused by Brexit.
Michel Barnier, the EU's chief Brexit negotiator, said the killing was "a reminder of how fragile peace still is in Northern Ireland. We must all work to preserve the achievements of the Good Friday Agreement."
Det Supt Jason Murphy, who is leading the investigation into McKee's death, described the act as "senseless and appalling beyond belief".
At a vigil in Derry on Friday, McKee's partner, Sara Canning said McKee's "amazing potential was snuffed out by this single barbaric act".
Irish President Michael D Higgins signed a condolence book at Belfast City Hall and spoke of the "outrage" in Ireland at the murder.
"The loss of a journalist at any time in any part of the world is an attack on truth itself," he said.