It's been more than a month since 22 people were killed in an attack at an Ariana Grande concert in Manchester, England.
And even though police arrested 22 people after the bombing, no one has been charged.
Police said those arrested were suspected of terrorism activities or of aiding the attacker leading up to the concert. Two were immediately found to have no involvement, and the rest were released without charges.
Now, the head of Manchester's counterterrorism police suspects more people could have been involved in plotting the attack.
The news comes as the U.K. deals with a wave of deadly terror attacks. In early June, three attackers ran a van through a crowd of pedestrians at London Bridge before stabbing several people at Borough Market. Eight people died.
A little over two weeks later, an attacker plowed a van through a crowd of worshipers outside a mosque in London. One person was killed.
The Manchester bombing is still under investigation; authorities say more arrests could be made as details unfold.