manchester arena

An official inquiry found that MI5, Britain's domestic intelligence agency, didn't act quickly enough on information that provided an opportunity to prevent the attack.

U.K. authorities are still trying to find the distinctive blue suitcase Salman Abedi was seen carrying as he moved around Manchester's city center.

Hours before the vigil, British Prime Minister Theresa May announced that another attack could be "imminent." From around the world, people expressed condolences for the bombing victims.

"It is a possibility we cannot ignore that there is a wider group of individuals linked to this attack," Prime Minister Theresa May said of the bombing that killed at least 22 people in Manchester.