All of the people arrested following the attack outside the U.K. Parliament last week have been released without charge, British police said.
A 30-year-old man, arrested in Birmingham on suspicion of preparing terrorist acts, was released Saturday, London Metropolitan Police confirmed. Eleven others who were swept up in the aftermath of the assault have already been freed.
Khalid Masood, 52, mowed down pedestrians on a bridge in central London before fatally stabbing a policeman outside the Houses of Parliament on March 26. The 82-second rampage ended when he was fatally shot by police near Parliament.
Four victims, including an American tourist, died in the car-and-knife rampage.
Police are yet to make any further arrests linking anyone else to Masood, who born Adrian Russell Ajao.
Deputy Assistant Commissioner Neil Basu previously said police believe he acted alone but wanted to establish whether he was "inspired by terrorist propaganda or if others have encouraged, supported or directed him."
Officers are actively investigating Masood's motive for the attack. British Prime Minister Theresa May told the House of Commons last week that he was known to security services as "a peripheral figure" and "was not part of the current intelligence picture."
Earlier this week, Masood's wife, Rohey Hydara, said she was "saddened and shocked," and condemned her husband's action.
Hydara wished a "speedy recovery" to the people hurt in the attack, in a statement given to police.
Among the injured is Utah woman Melissa Cochran, whose husband, Kurt, was the American tourist killed.
The Cochrans were touring Europe and stopped in London, where Melissa's parents are serving as missionaries for The Church of Jesus Christ of Latter-day Saints, when the attack occurred. In an update on the family's GoFundMe page posted Thursday, they say Cochran "is getting stronger every day."
She is seen standing with crutches and a brace on her left leg at a London hospital.
The coroner's formal inquest into the deaths of Masood's four victims was opened and adjourned on Wednesday. A provisional date for the pre-inquest review was set by the corner for May 19.