London Bridge stabbing suspect plotted 2010 attack on London Stock Exchange

The man suspected of carrying out a deadly terror attack near the London Bridge spent years in prison for plotting other attacks in the U.K., according to British counter-terrorism officials and a 2013 report from the U.K.'s counter-intelligence and security agency.

Usman Khan, 28, was imprisoned from 2012 to 2018 for planning attacks, including one aimed at the London Stock Exchange in 2010, the officials told ABC News.

Khan is believed to be the only suspect in the stabbing Friday afternoon that left two people dead and three others injured.

He was confronted by civilians, authorities said, whom officials and the greater public have called heroes.

Responding police officers shot Khan, who was wearing a fake suicide vest, to death, authorities said.

In 2012, nine men who were members of a terrorist network in England and Wales -- including Khan -- were sentenced for plotting attacks that were described as "al-Qaida inspired terrorism," according to a 2013 report from the U.K.'s counter-intelligence and security agency, MI5.

The report said that one of the attack plans was against the London Stock Exchange.

The men pleaded guilty and were sentenced to between five and 17 years, according to the report and an MI5 statement.

The British counter-terrorism officials also told ABC News that he had links to Pakistan's tribal areas and planned to run training camps there in an attempt to recruit others.

Neil Basu, assistant commissioner for the Metropolitan Police said, "Clearly, a key line of enquiry now is to establish how [Khan] came to carry out this attack."

He said in a statement that Khan had been released last December. Following his release, he was wearing an electronic tag, according to the counter-terrorism officials.

The Parole Board said in a statement that they understand why there is speculation regarding Khan's release, but had "no involvement" in it. The board said he had been released "automatically on licence (as required by law), without ever being referred to the Board."

The victims who were killed -- identified by police as a man and woman -- have not yet been identified. Those injured, two women and one man, remain in the hospital, according to Basu.

Police have confirmed that the attack began inside Fishmonger's Hall at an event and then continued onto the London Bridge. The attack inside the hall lasted for "a number of minutes," Basu said.

Basu noted that "there is no evidence to suggest anybody else is involved."

ISIS on Saturday called Khan an ISIS "fighter" and said he carried out the attack in response to the terror group's call to attack coalition countries. Authorities have not confirmed any affiliation with ISIS.

Khan had been living in the Staffordshire area, located about 161 miles northwest of the London Bridge, authorities said.

In the hours after the attack, police conducted a search of a home in Staffordshire.

Police have asked anyone with information to come forward, especially those were at Fishmonger's Hall.

London Bridge and some surrounding areas remained closed Saturday while forensic teams investigate the crime scene. Flags on government buildings will fly at half-mast in the U.K. in honor of the victims, the government said.

World leaders and politicians in the U.K. have expressed their condolences to the victims and condemned the attack.

Queen Elizabeth II said in a statement she and Prince Philip "have been saddened to hear of the terror attacks at London Bridge. We send our thoughts, prayers and deepest sympathies to all those who have lost love ones and who have been affected by yesterday's terrible violence. I express my enduring thanks to the police and emergency services, as well as the brave individuals who put their own lives at risk to selflessly help and protect others."

London Mayor Sadiq Khan said the city would "stay resolute in our determination to stand strong and united in the face of terror."

Prime Minister Boris Johnson called the attacks "appalling" in a tweet.

Johnson said in a later statement that Britain "will never be cowed or divided or intimidated by this sort of attack."

In June 2017, eight were killed when a group of attackers plowed a van into people on London Bridge and then drove to nearby Borough Market and stabbed several others.

ABC News' Dimitrije Stejic, Joe Simonetti, Morgan Winsor and Emily Shapiro contributed to this report.