Police are trawling hundreds of hours of CCTV and camera phone footage to piece together how a 12-year-old girl was stabbed to death in a busy shopping street in Liverpool. Ava White, an “incredibly popular” girl who had been made an “peace ambassador” in 2019, died after suffering “catastrophic injuries” on Church Street in the city centre on Thursday evening. Detectives believe she was out with friends to watch the annual Christmas lights switch-on when she became involved in a verbal argument that escalated into a knife attack, witnessed by numerous children. A group of boys were seen running away from Church Street as members of the public tried to save her life, police said. Paramedics attended and Ava was taken to Alder Hey children’s hospital, where she died a short time later. Four boys – one aged 13, two aged 14 and one aged 15, all from the Toxteth area of Liverpool – were arrested on Thursday evening and in the early hours of Friday morning at different locations, Merseyside police said. Ch supt Ngaire Waine said it was an isolated incident and no one else was currently being sought. Ava was a year 8 pupil at Notre Dame Catholic college in Everton. The headteacher, Peter Duffy, said: “Ava was a much-loved, valued and unique member of the Notre Dame family. She was an incredibly popular girl with a fantastic group of friends. “Our deepest thoughts and prayers go out to Ava’s family and friends and all those affected by this utterly tragic event. My staff are working with students to provide all the support they need at this traumatic time.” In 2019, Ava was given the Peace Ambassador award by Colin and Wendy Parry, of the Tim Parry Johnathan Ball Peace Foundation, whose son died in the Warrington IRA bomb in 1993. A large cordon remained in place in Liverpool city centre on Friday as forensic investigators gathered evidence. Floral tributes had been left at the scene, with residents coming to pay their respects and share their grief. Several children witnessed the attack, according to Alan Walsh, an anti-knife crime campaigner and youth worker. “I got a phone call at nine minutes past 12 … from a young person who was absolutely heartbroken and traumatised by what he saw. He wasn’t involved in it. He was just in town when he suddenly saw the girl’s friends screaming and shouting – it was heartbreaking,” he said. “When that phone call finished another four came through.” DS Sue Coombs said: “We know at the moment that Ava was with her friends in Liverpool city centre and there has been a verbal argument which has escalated to an assault on her involving a knife.” Coombs said officers were examining “hundreds of hours of CCTV” from the city centre. She also appealed for anyone with phone footage to contact police: “There were an awful lot of people in town because of the switch-on of the lights, so we’re asking if people would just check their phones really. While taking photos they may have picked up something of significance that they don’t even know yet.” Steve Rotheram, the mayor of the Liverpool city region, said: “Ava was just a child with her whole life in front of her. Her future has been stolen and the lives of her family and friends shattered. I am angry today for Ava and her family, for the parents across the region worrying about their children’s safety, and angry that such a heinous act should take place here.” Ava was one of two females to die in suspicious circumstances in Liverpool on Thursday, the same day the city launched a three-year strategy to tackle violence against women and girls. The mayor, Joanne Anderson, said: “This is an absolute priority for me and my administration.” A 47-year-old woman was found dead in a house in Stoneycroft in east Liverpool on Thursday afternoon. Three men, aged 21, 46 and 57, were arrested on suspicion of murder. The body of a woman in her 30s was also pulled from the River Mersey at Pier Head waterfront on Friday morning in an unrelated incident.