British police have arrested two men in connection with a mass stabbing aboard a London-bound train that injured 11 people.

Police responded to reports of knife attacks aboard a train from Doncaster, a city in the northeast of England, to London’s famous King’s Cross station at around 8 p.m. on Nov. 1. The train made an unscheduled stop in Huntingdon, a market town near the University of Cambridge, and police say they arrested two men on suspicion of attempted murder within minutes.

Ten people were taken to a nearby hospital by ambulance, and one other person later admitted themself to a hospital, according to police. Initial reports suggested nine people suffered life-threatening injuries, but four of those people have since been released from the hospital. Two remain in critical condition.

Passengers who spoke to the BBC recounted a bloody, gruesome scene. One passenger, Olly Foster, told the outlet he believed the stabbing was a Halloween prank when people initially began shouting. Soon, though, a man “covered in blood” walked into his train car and sat down.

"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.