Story highlights Four people died and dozens were injured in the March 22 attack

A 30-year-old man freed Saturday was among 12 people to be released

London (CNN) All those arrested in connection with last month's terror attack on Westminster Bridge and the UK Parliament have been released "with no further action," London's Metropolitan Police said Saturday.

A 30-year-old man previously arrested in Birmingham "on suspicion of preparation of terrorist acts" was freed Saturday, the police said in a statement.

In addition, 11 others who were previously arrested in connection with the attack investigation have all been released with no further action, police said.

The attacker, Khalid Masood , 52, was shot dead by a police firearms officer at the scene of the March 22 incident.

Four people died and dozens were injured in the attack as Masood plowed through pedestrians on Westminster Bridge before fatally stabbing a police officer who was guarding the Houses of Parliament. The entire episode lasted 82 seconds, police said.

Read More