Members of the public helped thwart London Bridge knife attacker Usman Khan with a fire extinguisher and a narwhal tusk before police shot him dead, The Guardian reports. One bystander used a narwhal tusk, another a fire extinguisher. At least one of the bystanders who fought back had done time for murder.

Though the attack ended on London Bridge, it actually began at Fishmongers’ Hall, a sort of museum and union hall on the north end of the bridge. Inside, a criminal justice conference was taking place, and Khan, wearing a fake suicide vest, threatened to blow up the building. He then began stabbing people randomly before fleeing outside to the bridge.

One of the men inside the building, a Polish chef identified only as “Lucasz,” fought back. He grabbed one of the artifacts on the walls, a five-foot narwhal tusk, and went outside to confront the attacker, lunging at him with the marine mammal’s tooth.

“A guy who was with us at Fishmongers Hall took a 5ft narwhal tusk from the wall and went out to confront the attacker… that man’s a hero,” said a bystander.

Another man, whose identity appears to remain unknown, grabbed a fire extinguisher and sprayed its contents at the attacker.

Another bystander, 24-year-old Thomas Gray, tackled Khan to the ground and then stomped on his left wrist, hoping to get him to release one of the knives Khan had been carrying. Gray called upon his years playing rugby in motivating him to stop the attack.

“I was brought up on rugby and the rule is ‘one in, all in’. I did what any Londoner would do and tried to put a stop to it,” Gray said.

Gray also said that “five or six other blokes [guys]” helped tackle and stomp on Khan.

Featured image credit: Chris J Ratcliffe Getty Images

One of the men who pinned down Khan was a convicted murderer. James Ford, 42, had been jailed since 2004 on charges of killing a mentally disabled woman, and was serving his time at an “open prison” in London. He rushed to the scene when the attack unfolded, helping pin down Khan. Further, authorities believe he helped save the life of a woman who was injured in the attack, although how he did that is unclear.

David Wilson, a professor of criminology at Birmingham City University, said that Ford’s heroism is evidence that people can change while in prison.

“I know through my work that people do change and they change as a consequence of innovative but challenging regimes such as the one at [the prison where Ford did some of his time],” he said.