British authorities said they have made two more significant arrests for the Parliament terror attack.
That brings the total number of people in custody for the Wednesday attack to nine.
Police said Khalid Masood, 52, plowed a car into a crowd on the Westminster Bridge Wednesday.
Investigators said they never linked Masood to any terrorism crimes, and had no reason to believe he would plan an attack.
"We remain keen to hear from anyone who knew Khalid Masood well, understands who his associates were and can provide us with information about places he has recently visited," Rowley said. "There might be people out there who did have concerns about Masood but did not feel comfortable for whatever reason in passing those concerns to us."
Masood was born in southeastern England and had most recently been living in the central city of Birmingham.
Masood drove his car into crowds of people on Westminster Bridge on Wednesday afternoon, killing three and wounding some 50, before stabbing a police officer to death at the Houses of Parliament. He was shot dead by police.
Rowley said two police officers targeted in the attack have significant injuries. Two other people also remain in critical condition, one with life-threatening injuries.
The latest victim, who died in the hospital on Thursday, was 75-year-old Leslie Rhodes from Streatham, south London.
The victims include American Kurt Cochran.
His death has been devastating for his friends.
"He was just one of those guys i mean, you just know, you wanted to be his friend within five minutes,” Bret Layton said.
Cochran and his wife were celebrating their 25th wedding anniversary.
