One individual aged 32 is currently the only suspect after multiple people were attacked with a knife on a rail service, police have confirmed.
A rail staff member remains in a life-threatening state following the attack on a service from Doncaster to London to London King's Cross, which halted in Huntingdon, just prior to 20:00 GMT on the weekend.
A individual aged 35, who was arrested at the scene, has been freed with no further action after it was claimed "with honest intent" that he had been involved in the incident. Police subsequently clarified this was incorrect.
Eleven individuals were cared for in hospital after the attack. On Sunday night, authorities confirmed 5 casualties had been discharged.
The police also confirmed the rail staff member in life-threatening state had tried to halt the assailant.
"Having examined the CCTV from the service, the actions of the member of rail staff were nothing short of heroic and undoubtedly saved people's safety," a spokesman said.
The suspect, who is from the city, entered the LNER train at the local station, the force reported.
"Our inquiry is moving at pace and we are certain we are not searching for anyone else in relation to the incident," stated a police official.
The force confirmed a blade had been recovered by officers at the scene.
A managing director expressed gratitude to emergency service workers "due to their swift and professional response" and said the organization and employees were "profoundly shocked and saddened" by the incident.
"The considerations and wishes are with all those impacted, particularly our staff member who remains in a life-threatening condition, and their loved ones," he commented.
'Individuals Were Getting Trampled On'
A passenger was on the train with a companion when she saw a individual stabbed by a man carrying what seemed to be a large blade.
"It seemed he had a purpose to stab anyone he encountered directly in front of him," she said.
"I saw blood everywhere - individuals were yelling, 'he's got a blade.'"
Ms Ostalski reported she witnessed someone being stabbed "five or six rows" from her, noting: "I might have been the next target. Individuals were being trampled on."
"It was a extremely crowded service, so passengers were just trying to run away from the attacker, and individuals were tripping, and people were standing on them. It was terrible."
After the conductor succeeded to unlock a exit at the station, people began to flee.
"I doubt I can travel on a rail service anymore," the passenger concluded.
The operator of the service has been identified as Andrew Johnson.
When the alarm was activated, Mr Johnson reportedly notified the control room to get the train diverted from the main line to the slow track, which has a stop at Huntingdon.
Mr Johnson's actions are believed to be why first responders were able to board the train so rapidly.
His quick thinking likely avoided the service from stopping in the remote area or having to go to the next station, which would have required ten to fifteen minutes.
A representative said the operator is "very shaken" but "good", and praised him for doing "exactly the correct action".
"The driver did everything he was instructed to do, at the appropriate moment and in the proper way," said a representative.
"He showed true courage, genuine dedication, and strong resolve in the toughest of circumstances."
A further observer, an individual, said: "I will say there were certainly many heroes on that day, several caring people who just aimed to assist those around them - people providing blankets, heat packs."
The witness said he saw one injured man who had been slashed in the face. He was told the person was "attempting to defend a young girl from being attacked".
"He took that injury to the face out of defense for her - that's true real selflessness, without a doubt."
"I saw several people smeared in blood, and observing how severe their wounds were, I realised this is an event extremely severe."
