British police said they now consider only one of the two men they arrested as a suspect in the mass stabbing on a London-bound train.
"Detectives investigating a multiple stabbing on a train in Cambridgeshire can this evening confirm a 32-year-old man who was arrested is now being treated as the only suspect," said a statement from British Transport Police.
He remains in police custody on suspicion of attempted murder, it said, adding that he was from Peterborough, where he boarded the train.
"A 35-year-old man from London who was also arrested at the scene has been released with no further action," it said.
Police were alerted to an emergency on board a train between Doncaster, a town in northeast England, and London's King's Cross Station - a typically busy route - at around 7:40pm last night.
Ten people were initially taken to the hospital, with four discharged shortly after.
One of the people wounded in the attack, a member of the rail staff who was on the train and tried to stop the attacker, remains in a life-threatening condition.
"Detectives have reviewed the CCTV from the train and it is clear his actions were nothing short of heroic and undoubtedly saved many people's lives," police said.
Five of those injured have been discharged from hospital.
"Our investigation is moving at pace and we are confident we are not looking for anyone else in connection to the incident," Deputy Chief Constable Stuart Cundy said in the statement.
Eyewitnesses initially thought UK train stabbing was Halloween prank
BTP Superintendent John Loveless has said there is nothing to suggest the attack was a terrorist incident.
He said counter-terrorism police had initially supported the operation but the incident was now not being treated as terrorism-related.
He said: "British Transport Police declared a major incident yesterday, and counter-terrorism policing were initially supporting our investigation.
"However, at this stage, there is nothing to suggest that this is a terrorist incident.
"This is a British Transport Police investigation, and we continue to work to establish at pace, the full circumstances and the motivations that have led to this incident.
"At this early stage, it would not be appropriate to speculate on the cause of this incident."
Britain's King Charles III and his wife Queen Camilla said they were "truly appalled and shocked to hear of the dreadful knife attack" on the train.
"Our deepest sympathy and thoughts are with those affected, and their loved ones," the King said and thanked emergency services for their response.
Britain's defence minister John Healey said the early indications are that it was "an isolated attack".
"The early assessment is that this was an isolated incident, an isolated attack," Mr Healey told Sky News this morning.
BTP said a major incident was declared, and at one point declared 'Plato', the code word used by police and emergency services when responding to a "marauding terror attack", before the latter declaration was subsequently rescinded.
One eyewitness told Sky News that one of the suspects was waving a large knife, before being tasered by police, while another, Olly Foster, told the BBC that he was on the train when someone ran past him saying someone was stabbing "everyone, everything".
"I put my hand on this chair...and then I look at my hand, and it's covered in blood. And then I look at the chair, and there's blood all over the chair. And then I look ahead and there's blood on all the chairs," he said.
An older man "blocked" an attacker from stabbing a younger girl, leaving him with injuries to his head and neck, Mr Foster said, adding other passengers used their clothing to try and stem the bleeding.
He said the incident "felt like forever".
Video footage on social media showed scores of blue-light police cars and emergency vehicles in a station car park, and a team of armed police running towards the stationary train at Huntingdon station.
Officers wearing forensic suits, with a police dog, could be seen on the platform.
Local MP Ben Obese-Jecty called it a "truly horrific incident".
"My thoughts are with all those victims who were injured during this heinous attack," he wrote on X.
British Prime Minister Keir Starmer described the incidents as "deeply concerning".
"My thoughts are with all those affected, and my thanks go to the emergency services for their response," he added.
LNER, which operates East Coast Mainline services in the UK, said disruption to its services between London Kings Cross and Lincoln, Doncaster, Leeds, Bradford Forster Square and Harrogate was expected to last until tomorrow, with passengers advised to defer their travel where possible.
David Horne, managing director of LNER, said in a statement: "We are deeply shocked and saddened by this serious incident, and our thoughts are very much with everyone involved.
"I would like to thank the emergency services for their quick and professional response and the care they have provided to those injured. Anyone with information who hasn't already spoken to police is urged to contact British Transport Police.
"The safety and wellbeing of everyone affected will remain our priority. We will continue to do everything we can to support our customers and colleagues during this difficult time."
A spokesperson for the Rail, Maritime and Transport union said: "We are horrified by the mass stabbing attack on an LNER train last night.
"Our thoughts remain with the train crew and passengers who were either at work or going about their business on a busy Saturday night during this awful incident.
"It is important we allow the emergency services and authorities to establish the full facts before commenting further."
