British Prime Minister Theresa May said Tuesday that officials know the identity of the attacker who killed 22 people at an Ariana Grande concert in Manchester on Monday night. Officials said the perpetrator acted alone and died at the scene, and have declined to release his name. Separately, police also tweeted Tuesday morning that they had arrested a 23-year-old man in South Manchester in connection with the attack. May said the bombing, which injured dozens about 10:30 p.m. Monday, was one of the worst the country has seen. “We struggle to comprehend the warped and twisted mind that sees a room packed with young children not as a scene to cherish but as an opportunity for carnage,” she said. “But we can continue to resolve to thwart such attacks in future. To take on the ideology that often fuels this violence.” May’s speech came as the first victim of the attack has been publicly identified: Georgina Callander, 18 years old, was reported by officials at her former school in the village of Croston to have died of injuries suffered in the explosion. The BBC reports the youngest victim was primary-school age, which is 4 to 11 years old in Britain.