Schools have beefed up security and police are warning the public amid fears a knifeman who attacked four random victims in London may still be at large. A 45-year-old woman is fighting for her life and two men in their 20s remain in hospital after a knifeman attacked people walking alone in Edmonton, in the north of the capital, during a 14-hour rampage on Saturday night and Sunday morning. Schools in the area have brought in extra security today and police have urged anyone walking on their own through the area to take extra care. Patrols were stepped up as detectives questioned two men, one of whom is in his 40s, on suspicion of GBH after they issued a description of a suspect as a tall, slim black man, possibly wearing a hood. But investigators are said to be unsure whether either of the men in custody is the knifeman and are therefore encouraging caution from those in the area. Crime scene: Plumber Roger Blackman (pictured right) helps police officers at the scene of the fourth London stabbing Police have warned the public to be on their guard following the stabbings in Edmonton from Saturday night into Sunday morning. Pictured: Emergency services attend to the Brettenham Road stab victim Police are now hunting for the knifeman after four people were stabbed in random attacks during a 12-hour north London rampage Roger Blackman was first on the scene to the final of the four stabbings and saw the attacker run off, leaving the victim with blood pouring from a wound. Speaking to MailOnline last night, he said: 'I heard a scream, I looked to my right, I saw a guy run off, then another scream. I saw blood pouring out of the back of him, I went to my van to get some towels to stem the flow. 'I saw the guy turn around and run off, he was literally about 10-15 feet away from where I was. I was in the back of my van so I'm always aware of what's going on around me. 'The victim was screaming, oh my God, oh my God, why has this happened to me. There was blood pouring out of his gash. It was a great big gash, about a three-inch wound. 'I was visiting my mum for mother's day. You hear about it in the papers and now it's happened in front of your mother's house. It does make you wonder, it makes you think about going out.' The first attack happened around 7pm on Saturday, with a 45-year-old woman stabbed in the back by the man. She is the most seriously injured and police described her condition as 'critical' this morning. Forensic investigators collect evidence from the scene of a stabbing in Edmonton after a spate of attacks Timeline of stabbings Saturday March 30 7.02pm: A woman, aged 45, is left in a 'critical condition' after she is knifed in the back on Aberdeen Road. Sunday March 31 00.15am: A man is stabbed in Park Avenue and rushed to hospital with non-life threatening wounds. 3.55am: A 23-year-old man is stabbed at Silver Street, Edmonton, before being found at Seven Sisters tube station. 9.43am: A man is knifed in the back on Brettenham Road in another 'bloodbath attack'. The second assault happened shortly after midnight that night, with a 52-year-old man attacked on nearby Park Avenue. He was rushed to hospital but has since been discharged, police revealed this morning. The third attack happened near Seven Sisters tube station shortly before 4am on Sunday, with a 23-year-old man injuried. He remains in a 'critical but stable condition'. The fourth attack happened around 9.45am on Sunday, with a 29-year-old male victim also stabbed in the back. He remains in hospital but doctors expect him to survive his injuries. Responding to parents' fears over safety this morning, the nearby Nightingale Academy tweeted: 'Please be assured have a stringent lock down procedure and protocol. 'We have staff on the gate each morning and evening and we have a full time police officer who works at the school. Please be assured the students safety is paramount.' Detective Superintendent Luke Marks, from the North Area Command Unit, said: 'Our investigation into these assaults is ongoing and, to date, our enquiries have resulted in two people being arrested. 'All four of the victims were assaulted from behind in the street in seemingly random attacks. Due to the proximity of the assaults, we still believe that a single suspect was involved and enquiries, including the review of CCTV footage, are ongoing. 'Two of the victims remain in a critical condition; and a third is receiving medical treatment. We are in contact with the fourth victim who has been discharged from hospital. 'I would ask that anyone with information come forward and contact us. I am also continuing to encourage people to remain vigilant, especially when walking alone. You will see uniformed patrols in the Edmonton area; if you have any concerns, please speak with my officers.' The attacks as Theresa May today hosted a summit to tackle the spiralling knife crime problem Home Secretary Sajid Javid and Met Police Commissioner were among those attending Opening a summit in Downing Street this morning, Prime Minister Theresa May said tackling knife violence is a 'priority' for ministers as well as families, young people and communities across the country. More than 100 experts will meet this week after the Government unveiled new plans which could see frontline workers in schools, hospitals and police stations accountable for failing to 'spot warning signs' of violent crime among young people. Home Secretary Sajid Javid floated the idea of a so-called 'public health duty' intended to help spot the warning signs that a young person could be in danger, 'such as presenting in A&E with a suspicious injury, to worrying behaviour at school or issues at home'. Sorry we are not currently accepting comments on this article.All rights reserved for this news site dailymail and under his responsibility