This is the moment police chased down a train to arrest a teenage boy on suspicion of murdering a nine-year-old schoolgirl.Footage captured the 16-year-old being detained by police after he fled onboard, having told a group of children at the station minutes earlier that he had accidentally killed someone.The defendant, who cannot be named for legal reasons, is accused of fatally stabbing Aria Thorpe in the chest with a knife at her home in Weston-super-Mare, North Somerset, on December 15, last year.He denies the charges of murder and manslaughter in relation to Aria's death, claiming her death was accidental.Footage released by Avon and Somerset police showed the teenager running down to the platform at Worle railway station and boarding a Great Western Railway service.An officer in pursuit sprinted after the suspect stopping the train as it began to pull away.Officers then boarded and handcuffed the teenager, who was wearing red tracksuit bottoms and a light blue coat, before escorting him off the train.Prosecutors said the defendant left Aria after stabbing her and was caught on CCTV telling a group of youths it was an 'accident', claiming she had 'walked or run into the blade of the knife he had hold of.' CCTV footage captured a 16-year-old flee to Worle railway station and board a train after fatally stabbing a nine-year-old schoolgirl Police rushed to the station and detained the teenager who was sat on a train attempting to escape The teenager, wearing a light blue coat and red tracksuit bottoms is escorted down the carriage in handcuffs by policeThe force also released a chilling 999 call made by one of the youths who had spoken to the teenager which alerted officers to his attempted escape.On the call, the boy told police handlers: 'There's some kid, and he's saying that he's stabbed her, and that she's dead on the middle of the floor, and he's ran out.'He said that he's going to get on a train to Highbridge.'The caller then told the police what platform he was on and said he was 'shaken up', before describing the suspect, who was 15 at the time, and confirming the rest of the group was safe.Giving evidence in Bristol Crown Court, the defendant said he picked up the knife from the kitchen and went into the lounge where Aria was sitting on the sofa.As she stood up, the teenager began waving the knife around and intending, he said to 'scare her, to get a reaction,' He told the jury: 'I leaned forward, acted like I was fencing.' The teenager then stabbed Aria who put her hand to her chest and collapsed to the floor. Minutes before attempting to flee on a train the teenager, pictured, told a group of youths that he stabbed someone Aria Thorpe was fatally stabbed in the chest with a knife at her home in Weston-super-Mare, North Somerset, on December 15 last year'I thought she had died,' he said. 'I got scared, I panicked. So I ran to the kitchen with the knife and I put it back into the sink.'The boy confirmed that he did not check on Aria or call an ambulance after he stabbed her.Aria's body was found lying face down by Ollie Sheppard who told the court he thought she was 'just missing around' before spotting blood and calling 999.He performed CPR on the schoolgirl until the paramedics arrived but Aria was pronounced dead just before 7pm on 15 December last year.Prosecuting, Ray Tully KC had earlier told the jury: 'He said she impaled herself in effect on the blade of the large kitchen knife. It follows what he is saying that he accidentally killed her.'Mr Tully said the defendant spoke to a group of children he knew around the rain shelter before attempting to escape on a train.In one interaction, the defendant asked to borrow a phone before telling a youth that he had to 'getaway,' the prosecution said.On the borrowed phone, the teenager searched: 'what happens if I killed someone?', the prosecution added. The teenager also told one of the children on the platform that he had a blade in his hand and that Aria 'ran into the knife.'Mr Tully continued: 'He kept saying it was an accident.'The suspect was later interviewed by police where he gave a prepared statement. He told police: 'I don't know why I did it - it just happened.'The prosecution said that during his prepared statement or interview there was no mention of Aria 'walking or running into the blade.'When asked what had been going through his mind, he said: 'I dunno.'Prosecutors said he did not check on her before fleeing but claims he was 'scared' and upset.Asked if he regretted his actions he 'nodded' and said: 'I wished I never did it.'