A individual aged 32 is now the sole person of interest following multiple people were attacked with a knife on a rail service, police have stated.
A rail employee remains in a critical condition following the attack on a service from Doncaster to London to London, which stopped in Huntingdon, just before 20:00 GMT on the weekend.
A 35-year-old man, who was arrested at the location, has been freed with no charges after it was reported "with honest intent" that he had been implicated in the incident. Officers subsequently clarified this was not the case.
Eleven individuals were treated in hospital after the stabbing. On Sunday evening, authorities stated five casualties had been discharged.
The force also stated the rail staff member in critical state had attempted to halt the assailant.
"Having viewed 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 individual, who is from Peterborough, entered the LNER service at the city's station, the force said.
"Our inquiry is moving at pace and we are certain we are not searching for anyone else in relation to the event," stated a police official.
The force said a blade had been found by police at the location.
A managing director expressed gratitude to first responders "for their swift and professional actions" and said the company and employees were "profoundly shocked and saddened" by the event.
"Our thoughts and wishes are with all those affected, particularly our staff member who remains in a life-threatening condition, and their family," he said.
'People Were Being Trampled On'
Amira Ostalski was on the train with a companion when she witnessed a individual stabbed by a individual holding what appeared to be a big kitchen knife.
"It seemed he had a mission to attack anyone he encountered directly in front of him," she stated.
"There was red everywhere - people were screaming, 'he's got a knife.'"
Ms Ostalski said she observed an individual being stabbed "five or six rows" from her, adding: "I could have been next. Individuals were getting crushed."
"The train was a very busy train, so people were just attempting to run away from the attacker, and individuals were falling, and people were standing on them. The situation was horrible."
Once the staff member managed to open a exit at the station, people began to flee.
"I doubt I'll be able to travel on a train again," Ms Ostalski added.
The operator of the train has been identified as the individual.
When the alarm was raised, the driver reportedly notified the operations center to get the train rerouted from the main line to the slow track, which has a platform at the station.
Mr Johnson's decisions are believed to be why first responders were able to access the train so quickly.
His quick thinking likely avoided the train from stopping in the middle of nowhere or having to go to the next station, which would have required ten to fifteen more time.
A trade union officer stated the operator is "quite shaken" but "good", and commended him for doing "precisely the right thing".
"The driver did everything he was instructed to do, at the right moment and in the proper manner," said a representative.
"He demonstrated real courage, real dedication, and strong determination in the toughest of circumstances."
Another witness, Thomas McLachlan, stated: "I will say there were definitely many brave individuals on that day, many caring individuals who simply wanted to assist those around them - people handing out blankets, hand warmers."
The witness said he saw one injured man who had been cut in the head. He was told the individual was "trying to protect a child from being harmed".
"The individual received that injury to the head out of defense for her - that's true genuine selflessness, right there."
"I saw multiple individuals smeared in blood, and observing how serious their injuries were, I understood this is an event extremely bad."
