Jane Onyanga-Omara, and John Bacon

USA TODAY

LONDON — A British man described by the Islamic State as one of its soldiers was named by police Thursday as the terrorist who unleashed a one-man wave of murder and mayhem on the city's famous Westminster Bridge and Parliament square, killing four and injuring dozens.

Khalid Masood, 52, has a lengthy rap sheet but no known terror convictions, police announced.

An American tourist was among the fatalities in Wednesday's carnage, his family said Thursday. The Islamic State, also known as ISIS, claimed responsibility for the attack, calling Masood its "soldier."

Eight people were arrested on suspicion of preparation of terrorist acts, and police said the investigation was continuing. Masood, fatally shot by officers at the scene, had a "range" of previous convictions for assault, possession of offensive weapons and other offenses, London Metropolitan Police said in a statement.

"Masood was not the subject of any current investigations and there was no prior intelligence about his intent to mount a terrorist attack," the statement said.

Masood plowed his car into a crowd on the iconic Westminster Bridge before ramming his vehicle into a gate outside Parliament and fatally stabbing a police officer, authorities said.

Metropolitan Police said the latest victim, a 75-year-old man, died Thursday in the hospital. Among the other fatalities included a Utah man on a trip with his wife to celebrate their 25th wedding anniversary, his family confirmed Thursday. Kurt Cochran's wife, Melissa, was hospitalized with serious injuries in the attack.

"A great American, Kurt Cochran, was killed in the London terror attack'" President Trump tweeted. "My prayers and condolences are with his family and friends."

Also killed were Keith Palmer, 48, the police officer with 15 years of service, and Aysha Frade, a British mother and schoolteacher.

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Before Masood was publicly identified, Prime Minister Theresa May said the attacker was British-born and known to security officers. She said the man had been investigated by MI5, the domestic security agency, "some years ago" regarding concerns about violent extremism.

"He was a peripheral figure. The case is historic — he was not part of the current intelligence picture," she said, adding there was "no prior intelligence of his intent or of the plot."

The prime minister said the best response to the attack was "millions of acts of normality."

“This country will not be cowed by these terrorists," she said.

May's call was heeded. Tourists streamed across Westminster Bridge on Thursday, hours after it was reopened to pedestrians and traffic. Stuart Elliott, 62, and his wife Vilma Elliott, 59, from Newcastle in northern England, were in London celebrating their 40th wedding anniversary. They traveled to the British capital Thursday morning.

"We were shocked, definitely," said Stuart Elliott, a gas technician. "But life just carries on."

"It was all booked for us to come," his wife added.

Hundreds of people gathered Thursday as dusk fell in Trafalgar Square in central London for a vigil to remember the victims.

Speakers included Home Secretary Amber Rudd and Sadiq Khan, the mayor of London. Many people lit candles.

Ken Hooper, 62, a retired police officer with Surrey Police, a county just south of London, wiped away tears following the ceremony.

"The whole thing is absolutely despicable," he said. "I came here to pay my respects. We'll go on for their sakes. It's unbelievable. We'll all pull together and they won't win. When a police officer is killed, it's awful to hear. It's like family."

Chris Kay, 31, a seminars manager in the legal industry who works nearby, said when the attack happened, "the first thing that went through my mind is how is this city going to react. Hopefully it will bring everyone together and make us stronger."

Mike Kelly, 63, a retired teacher, travelled from the county of Kent, south of London, specifically for the vigil.

"I came because when I heard the prime minister this morning say 'we are not afraid,' I thought 'she's quite right'."

He said his son is a detective in the Metropolitan Police and is working on the investigation. He applauded the emergency services for their response, and said he would continue as normal.

"These people won't prevail," he said.

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British media reported the car used in the attack — a gray Hyundai i40 — was rented in Birmingham, a city of more than 1 million people about 125 miles northwest of London. Anti-terrorism forces swept into the city, and seven of the suspects were arrested there.

Queen Elizabeth II said she and her husband, Prince Philip, would not be able to officially open New Scotland Yard, the London police headquarters, as planned Thursday "for very understandable reasons."

"My thoughts, prayers, and deepest sympathy are with all those who have been affected by yesterday's awful violence," she said in a message to Craig Mackey, the acting commissioner of the Metropolitan Police.

Of the 40 people injured in the incident, 29 required hospitalization and five remained in critical condition late Thursday. May said 12 Britons were taken to hospitals. The others include three French teenagers, two Romanians, four South Koreans, one American, one German, one Pole, one Irish, one Chinese, one Italian and two Greeks, she said.

Three police officers were injured as they returned from an event to recognize their bravery, May said, adding two were in serious condition.

Both houses of Parliament resumed normal operations Thursday. A minute's silence to honor the victims was held shortly after 9:30 a.m. local time. The crime scene and surrounding area remained cordoned off and police asked people to steer clear of the areas close to Parliament. A candlelit vigil will be held in Trafalgar Square later Thursday, the office of London's mayor announced.

"We are not afraid," May said in her address to Parliament. "Our resolve will never waiver in the face of terrorism. And we meet here, in the oldest of all Parliaments, because we know that democracy — and the values it entails — will always prevail."

Onyanga-Omara reported from London; Bacon from McLean, Va. Contributing: Kim Hjelmgaard, USA TODAY; Michael Settle, The (Glasgow) Herald