Two men arrested for the murder of Lyra McKee are 'members of the New IRA' says the detective leading the hunt for the journalist's killers.
Detective superintendent Jason Murphy added that a new breed of terrorist is coming through the ranks in Northern Ireland.
The two men, aged 18 and 19, were earlier arrested under the terrorism act in connection with the shooting of the 29-year-old journalist, who was killed as she covered rioting in Londonderry on Thursday night.
Detective Murphy said: 'What we are seeing is a new breed of terrorist coming through the ranks and that for me is a very worrying situation.'
However, he added that there had been a sea change in community attitudes and that was demonstrated in the revulsion expressed by many at Thursday evening's killing.
The detective explained: 'There is a real sense after what happened to Lyra of a sea change and I want people to have confidence to come forward and help us.
'The individuals responsible for Lyra's murder continue to hide in the shadows.'
DS Murphy also said they had offered no explanations for their actions to her family but police were working to bring about a positive change.
'This will be Lyra's legacy. Lyra's murder was not just an attack on Lyra, it was an attack on the fabric of this community.
'Lyra's killers have succeeded in only one thing, and that is in uniting the entire community in condemnation.'
'This morning we arrested two young men aged 18 and 19.
'I believe both of those are members of the New IRA, I believe both were involved in the attack on Lyra.
'Clearly my consideration is whether those two individuals acted in isolation or in collusion with other individuals, and I am keen for the community to come forward and help me answer that question.'
However, he said there was still fear of reprisals from the shadowy figures for giving information.
'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.'
A gunman aiming to kill police shot Ms McKee in the head after he fired indiscriminately during disturbances in the Creggan estate.
The arrests come after the 'New IRA' claimed that the gunman was 'attempting to protect' Creggan estate from 'heavily-armed' police during the riots.
Police earlier released CCTV footage of the masked gunman suspected of having shot dead the young journalist and it shows Lyra in the crowd lifting her phone to take pictures just moments before she was killed.
As the footage moves on, a masked gunman is shown lurking near the corner of a nearby building. The man is then spotted later on in the same area just moments before he takes aim at officers.
Police in Ireland have called the killing 'senseless and appalling' after Lyra, from Belfast, was shot in the head by suspects, believed to be dissident republicans linked to the New IRA, as they clashed with police on the Creggan estate.
Saoradh, a political party that reflects New IRA thinking, released a statement blamed the murder on an 'incursion' by 'heavily armed crown forces' in the Creggan estate, and that the gunman was 'attempting to defend people' from police officers.
Rioting had erupted following raids by police, who said they were trying to prevent militant attacks planned for Easter weekend, a time when dissidents are traditionally active due to the anniversary of the 1916 Easter Rising.
A senior detective leading the case has said the only way to find those responsible is if the community helps.
Detective Superintendent Jason Murphy said: 'People saw the gunman and people saw those who goaded young people out onto the streets, people know who they are.
'The answers to what happened lie within the community. I am asking people to do the right thing for Lyra McKee, for her family and for the city of Derry/Londonderry and help us stop this madness.'
He added that her death was 'senseless and appalling beyond belief' and highlighted that it represents the tragic loss of promise and 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. '
Police have urged those who have footage to send it directly to them, in order to aid their investigation and prevent further distress to Lyra's family and the local community.
Yesterday Sara Canning, the girlfriend of Lyra, who was shot dead while covering a riot in Londonderry, called for peace so that her beloved partner's death is 'not in vain'.
Ms Canning paid tribute to 29-year-old partner in front of hundreds of people attending a vigil in her memory and described her killing as a 'senseless murder'.
Ms McKee, 29, was hit by a stray bullet after a masked gunman opened fire towards a crowd of police officers and bystanders at around 11pm, as republican dissidents rioted in the city's Creggan estate.
Police in Northern Ireland confirmed they are hunting 'multiple suspects' after they blamed the New IRA for the murder of the journalist.
Speaking at the vigil, Ms Canning said: 'It has left so many friends without their confidante. Victims and LGBTQI community are left without a tireless advocate and activist and it has left me without the love of my life, the woman I was planning to grow old with are all passed in the loss of Lyra.
'Our hopes and dreams and all of her amazing potential was snuffed out by this single barbaric act.
'This cannot stand, Lyra's death must not be in vain because her life was a shining light in everyone else's life and her legacy will live on and the life that she has left behind.'
The latest winner of the Man Booker prize paid a tearful tribute to the murdered Belfast journalist.
Milkman author Anna Burns was among hundreds who turned out at Belfast City Hall for a vigil to Lyra McKee and stood for a minute's silence, which was followed with applause.
The books of condolence for Ms McKee was brought to the front steps of the building after the doors were officially closed for the night to allow those waiting in a long queue to sign it.
A smiling photograph of the 29-year-old journalist gazed across the rainbow flag-draped table which held two condolence books for well wishers to sign as well as a small posy of forget-me-nots.
Those attending were asked to talk to each other in memory of Ms McKee who they were reminded, loved conversations.
John O'Doherty of the Rainbow Coalition read out Ms McKee's 'Letter To My 14-year-old Self', in which she had written evocatively about facing challenging times at school and the moment she came out as gay to her mother, and relief when her mother embraced her.
Next three friends of Ms McKee's, who had been due to meet her for dinner that evening, shared their memories of their friend.
Michele Devlin, Anna Burns and Alison Miller supported each other as they tearfully addressed the vigil.
Ms Burns described Ms McKee as a 'dear, dear friend' that she had met through their mutual publisher Faber and Faber.
'It's absolutely wonderful that you are all here for Lyra,' she told the crowd, many of whom held candles.
'She was just so helpful and generous, her wee heart was always open.'
Irish and British politicians widely condemned the murder, with the city mayor John Boyle claiming: 'It doesn't matter if you call it Derry of Londonderry; this city is united with one voice... against this heinous murder.'
Yesterday, residents of the area walked past a wall which was plastered with graffiti which read 'IRA are done, defeated army'.
There still appeared to be a heavy police presence in the area which police trucks being parked along main roads and in residential areas.
Tributes including flowers and heartfelt notes were also left at the scene of the shooting. One single bunch of flowers was left on some steps, which bore a sign above it which read 'injury to all'.
Officers continued to inspect the scene while others were also pictured paying their own tributes to the journalist at various shrines and memorials which had been put up in her memory.
Defiant residents of the city later started the hashtag #NotInMyName on social media in an act of opposition to the violence, while hundreds of people attended a vigil in memory of the Belfast-born journalist near where she died.
Moments before her death, Ms McKee had posted an image from the scene of the riots on Twitter that showed smoke rising into the air above police vehicles, along with the caption: 'Derry tonight. Absolute madness.'
In another heartbreaking Tweet, she spoke of 'falling in love with Derry' and 'a woman who hails from it', before tragically adding: 'Here's to good times ahead and saying goodbye to bombs and bullets once and for all.'
Tributes left on a fundraising page said Ms McKee 'just wanted to expose the truth' and was an 'incredible investigative journalist and a defender of press freedom'.
Her first book, Angels With Blue Faces, is a non-fiction investigation of the murder of Robert Bradford, a Methodist minister and Ulster Unionist MP for South Belfast who was killed by the IRA in 1981.
One person wrote on the page: 'Lyra was a passionate defender of press freedom and exposing the truth. You don't expect journalists to be killed anywhere.
'For it to happen to a friend, in a (troubled) democracy, is just unbelievable.'
Deputy Chief Constable Stephen Martin said that police were hunting multiple suspects following the shooting, but refused to be drawn on suggestions that the gunman who killed Ms McKee was a teenage boy.
Speaking during an emotional press conference at the Guildhall in Londonderry on Friday, he said: 'We certainly believe there was more than one person who was involved in this last night.
'Obviously only one person pulled the trigger but there was more than one person. This was not done to further any cause - this will have achieved nothing other than to plunge a family into grief.'
Ms McKee had covered the legacy of the Troubles extensively, and spoke of being segregated from Protestants while growing up on Belfast's 'Murder Mile', a road notorious for the high number of locals killed by Ulster loyalists.
Assistant chief constable Mark Hamilton said more than 50 petrol bombs were thrown at police during the riots as he described the killing as 'not only a murder of a young woman, it is an attack again on the people of this city'.
He then pointed the finger at the New IRA, an amalgamation of dissident republican factions in the city, which was blamed for a car bombing in Bishop Street in January, as he called for calm in the city ahead of Easter.
Speaking about the shock of Ms McKee's death, close friend Matthew Hughes told MailOnline: 'The loss her friends feel is unquantifiable. Unfathomable. She is utterly irreplaceable.'
Paying tribute to his friend, he added: 'It was just after midnight, my wife got a call from Lyra's partner. It was probably the one of the worst phone calls I've ever overheard in my life.
'I heard the word 'shot', and that she was dead. Lyra was one of my best friends, she was a groomswoman at my wedding; she helped me tie my tie before the wedding. We'd traveled abroad together; we were very, very close.'
Mr Hughes said he had known Ms McKee for five years and understood his friend had been killed by a stray bullet, according to Ms McKee's partner, who was at the scene.
He added: 'Lyra was such a brilliant, kind, compassionate person, and so unbelievably good; as a journalist, as a storyteller, as a person.
'If she saw a homeless person on the street she would go and buy them a cup of tea and a sandwich. She was the kindest, brightest, most determined person.
'She was a great investigative reporter, and she was at this inflection point in her career - she was going to go to the next level, she was so bright and so accomplished.'
Ms McKee was an editor for California-based news site Mediagazer and had extensively covered the Troubles in Northern Ireland, leading to Forbes naming her as one of its 30 under 30 in the media in 2016.
She first rose to prominence in 2014 after a blog post called 'Letter to my 14-year-old self' in which she spoke about the struggle of growing up gay in Belfast.
Last year, she released her first novella called Angels With Blue Faces, a non-fiction novella about the murder of a reverend during the Northern Irish conflict, with her second book The Lost Boys scheduled for release in 2020.
In a forward to her first book, she said her share of the sale proceeds would 'go to Paper Trail, a charity that helps survivors of the conflict – regardless of religion, political belief, or other affiliations'.
She added: 'It empowers victims by helping them ask questions and obtain answers about what was often the most traumatic experience of their lives.
'Your money will help Paper Trail continue to do this, as Northern Ireland continues to recover from the devastation left by 30 years of war.'
In the foreword, she spoke of her country as 'a beautiful tragedy, strangled by the chains of its past and its present'.
'It's a place full of darkness and mysteries,' she added. 'It's also my home. Sometimes, I love it and hate it in equal measure.'
She had headed to the city's Creggan district after riots erupted following police raids on a number of homes yesterday.
Several vehicles were hijacked and set alight earlier in the incident before the gunshots were heard.
Another reporter, Leona O'Neill, said she was standing next to the woman who was hit. She Tweeted: 'I was standing beside this young woman when she fell beside a police Land Rover tonight in Creggan.
Michelle Stanistreet, National Union of Journalists (NUJ) general secretary, said Ms McKee was one of the most promising journalists in Northern Ireland.
She said: 'A young, vibrant life has been destroyed in a senseless act of violence. A bright light has been quenched and that plunges all of us in to darkness.'
Writer Brooke Magnanti, whose blogs were made into TV hit Secret Diary Of A Call Girl, said she was 'stunned' by the news.
She tweeted: 'I only knew her from online and a phone conversations after we were introduced by @GlasgaeLauraLee.
She struck me as a thoughtful journalist unafraid to challenge her own beliefs. Rare and precious. Deepest condolences to family and friends.'
The unrest comes ahead of the Easter weekend where republicans mark the anniversary of the 1916 Easter Rising, a time when dissidents are traditionally active.
Irish Taoiseach Leo Vardakar said his government condemned the violence in the 'strongest possible terms'.
He tweeted: 'The Government condemns in the strongest possible terms the fatal shooting of journalist and writer Lyra McKee in Derry.
'We are all full of sadness after last night's events. We cannot allow those who want to propagate violence, fear and hate to drag us back to the past.
'I would like to express my sincere condolences to Lyra's family, her partner Sara and her friends.
'Our solidarity also goes out to the people of Derry and to the entire journalism community.'
United States House of Representatives speaker Nancy Pelosi also paid tribute to journalist Ms McKee during a visit to Stormont.
A minute's silence was observed during an event she attended in the Long Gallery in respect of Ms McKee during a speech by Northern Ireland Assembly speaker Robin Newton.
During her speech, Ms Pelosi said: 'Sadly, Mr Speaker, we join you on the sadness of the tragedy that happened last night, we extend our condolences to the family and your moment of silence at this time, on Good Friday is especially poignant,' she said.
'You not only had a moment of silence, you presented a sense of resolve that justice would be done and the memory of that young woman would be a lesson for all of us.'
Sinn Fein deputy leader Michelle O'Neill said the killing in Derry was a 'senseless loss of life'.
