Two teenage men were arrested under the Terrorism Act related to journalist Lyra McKee's killing, Police Service of Northern Ireland announced Saturday.
Speaking to media in Londonderry on Saturday afternoon, Detective Superintendent Jason Murphy said they arrested this morning two teenagers, aged 18 and 19, under the Terrorism Act and conducted a number of searches as part of the ongoing investigation into Lyra's murder.
"Shortly before 11 pm on Thursday night, 29 year old Lyra was murdered by terrorists. I believe that the people responsible are members of the new IRA," Murphy said.
Murphy said terrorists were "lurking in the shadows". He warned: "What we are seeing is a new breed of terrorist coming through the ranks and that for me is a very worrying situation."
He said Lyra was killed by shots that were fired indiscriminately in Fanad Drive. "The brutal nature of the attack has sent shockwaves around the world. The shots were fired in a residential area at a time when there were large numbers of local people on the street including children. The gunman showed no thought for who may have been killed or injured when he fired these shots."
One eye-witness described how a masked gunman came round a corner and fired shots indiscriminately towards police vehicles.
"There were a number of houses with families - they had all spilled out on the street to see what was happening. There were young people, there were children on the street, there were teenagers milling about and a gunman just fired indiscriminately up the street," the witness told the BBC.
Police were bombarded with at least 50 petrol bombs, while a number of vehicles were ambushed and set on fire in what has been some of the worst violence seen in Northern Ireland for some time.
The Irish border area was a flashpoint during the decades of conflict that cost over 3,600 lives after the 1960s. The Irish Republican Army (IRA) waged a campaign for the reunification of the island, leading to 30 years of what is known as "the Troubles." It laid down its guns in favor of pursuing a political solution in 1998.
Thursday's violence broke out after police were carrying out a search operation looking for firearms that may have been used over the Easter weekend, which marks the anniversary of the 1916 Easter Rising, a time when dissidents are traditionally active.
Murphy described Lyra's death as senseless and appalling beyond belief. "It represents the tragic loss of promise and the loss of potential, however it should not be the loss of hope. We know that the people of Creggan do not support what happened and they stand with us today in outrage and disgust at the mayhem that took place on their streets," he said.
He said there had been a sea change in community attitudes which was demonstrated in "unprecedented support" for police investigating the killing.
"Lyra's murder was not just an attack on Lyra - it was an attack on the fabric of the community. Lyra's killers have succeeded only in uniting the entire community in condemnation," Murphy said, urging witnesses who had yet to come forward to not be deterred by intimidation.
British Prime Minister Theresa May said in her twitter Friday that the death of McKee is "shocking and truly senseless." She expresses deepest condolences to McKee's family, friends and colleagues and said "she was a journalist who died doing her job with great courage."
Northern Ireland Secretary Karen Bradley visited Londonderry on Saturday and signed a book of condolence.
She wrote: "A tragic loss, such promise, such energy, so much potential. We can only imagine what you would have achieved."
In Dublin, Irish Prime Minister Leo Varadkar said: "Our solidarity also goes out to the people of Derry and to the entire journalism community.We cannot allow those who want to propagate violence, fear and hate to drag us back to the past."