Investigators are looking for a motive behind an attack in the German city of Wuerzburg in which a man armed with a knife killed three people and wounded at least five others.

The suspect, a 24-year-old Somali, was shot in the leg by police and arrested after the Friday afternoon attack in the southern city’s central area.

Police said the man’s life is not in danger and he is being questioned in a hospital.

Bavaria’s top security official, Joachim Herrmann, said the suspect had been known to police and had been admitted to a psychiatric unit a few days earlier.

He told the dpa news agency that he could not rule out an Islamic extremist motive, because one witness had reported hearing the suspect shout: “Allahu akbar,” Arabic for: “God is great.”

The man had lived in Wuerzburg since 2015, most recently in a shelter for the homeless. He apparently did not know the victims.

Videos posted on social media showed pedestrians surrounding the attacker and trying to hold him at bay with chairs and sticks.