London – Authorities in London were facing tough questions Saturday as they pieced together events that led to two people being killed in a terror attack near London Bridge on Friday. Three others were injured.

The suspect in the attack was 28-year-old Usman Khan, a convicted terrorist who had been deemed a threat to the public, CBS News' Holly Williams reports. He was convicted on terrorism charges, part of a group that plotted to blow up the London Stock Exchange. He was jailed in 2012 and released in 2018, early.

The British media is reporting that Khan agreed to wear an electronic monitor. He was on probation.

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Many are asking why he was released from jail early.



"I have long argued that it is a mistake to allow serious and violent criminals to come out of prison early," said British Prime Minister Boris Johnson.

London's police counterterrorism chief said Khan was attending a program working to educate prisoners when he launched the attack on Friday near the site of a deadly rampage that unfolded in 2017, The Associated Press reported.

Khan was armed with a knife and wearing what police are calling a hoax suicide vest. He was apparently a lone attacker.

In an exclusive video from the Daily Mail, bystanders can be seen fighting him with fire extinguishers. They tackled him to the ground – an act of breathtaking heroism, according to London's mayor. A plainclothes police officer removed his weapon, and police shot and killed him at close range.

The attack was the first in the United Kingdom since 2017, said Richard Walton, the former head of counterterrorism for the London police and a CBS News consultant. There have been 22 disrupted terrorist plots in the U.K. in the last 18 months to two years, he said.

A house outside of London was searched overnight in connection with the attack.

Forensic workers attend the scene on London Bridge in London, Saturday, Nov. 30, 2019. Alberto Pezzali/AP

Editor's Note: This article has been updated to reflect that Khan was convicted on terrorism charges, part of a group that plotted to blow up the London Stock Exchange.