LONDON—The knife-wielding assailant who killed two people—and was then taken down by heroic passersby on London Bridge—was a convicted terrorist who was paroled last year.

Usman Khan, 28, pleaded guilty in 2012 to a plot to bomb the London Stock Exchange, Westminster Abbey, and Big Ben. He was freed in December 2018, on condition he wear a tracking device.

On Friday, he was attending a Cambridge University criminal justice symposium at Fishmongers’ Hall when he reportedly threatened to blow it up and then embarked on a stabbing rampage.

The harrowing incident ended on the same bridge where three terrorists killed eight people in 2017 when Khan—who was wearing a hoax suicide vest—was tackled and disarmed by members of the public as police arrived.

A tour guide told The Telegraph that he was driving when he saw the commotion on the bridge and stopped the car to run over.

“There were about five guys there when we got there,” he said. “I jumped in and kicked him in the head to make him release his knife. A few others did so. He was shouting, ‘Get off me, get off me.’”

He said that when the attacker was rolled over, they saw what appeared to be a bomb vest.

“The police arrived so quickly. They told us ‘get the fuck back.’ They had rifles. They put three rounds into him,” he said.

Cellphone footage of the incident showed armed police officers pulling people off the attacker, who was struggling to break free. One officer from the City of London police then shot the man at the northern end of the bridge. He died at the scene.

Neil Basu, head of counterterrorism at Scotland Yard, said the man was wearing a hoax suicide vest. “It has been declared a terrorist incident,” he said.

Basu indicated that the police had been warned that the man may have been wearing an improvised explosive device before they got to the bridge. Footage captured by various people in the vicinity, shows the firearms officer shooting the attacker as soon as he had a clear shot.

A member of the public who had carried the knife out of reach of the attacker could be seen motioning for other people walking across the bridge to stay clear of the melee, before the officer fired the fatal shot.

Police say a number of people were stabbed by the attacker, but they have not said how many, or given any details of the severity of the injuries to the survivors. One eyewitness called in to Britain’s Sky News to say that he had seen one of the victims. “A lady was being carried away from the scene,” he said.

London Mayor Sadiq Khan said the people who risked their lives to subdue the attacker had shown “breathtaking heroism.”

“What was amazing about today was we saw in the one individual—the suspect—the worst of humanity but we also saw in the response from members of the public, but also our emergency services, the best of humanity,” he said. “The message I want to send not just to Londoners, not just to visitors to our city but the rest of the world is that we are resolute in the face of terrorism and will not allow anyone to divide us.”

London has not suffered any major terror incidents since the previous London Bridge attack, which took place a few days before the 2017 general election.

In that attack, three men with large knives and fake suicide vests drove a truck into members of the public on the bridge before running towards Borough market on the south bank of the Thames, brandishing the knives and stabbing people who were out for the night in the area’s bars and restaurants. Counterterror police ordered Borough market to be evacuated as Friday’s incident unfolded but there was only one attacker on this occasion.

Prime Minister Boris Johnson cut short an election campaign trip to his own district of Uxbridge in northwest London to return to Downing Street for a briefing on the attack. Britain will go to the polls on December 12.