A man who reportedly set people on fire in Boulder, Colo., on Sunday injured several victims— some critically — triggering the evacuation of a large portion of the city’s downtown.

The assailant was arrested, Boulder Police Chief Stephen Redfearn said at an afternoon briefing, adding that investigators were gathering more information on him before releasing his name.

Details were scant as police processed the scene, closed businesses and asked people to avoid the area .

While FBI director Kash Patel called it a terrorist attack on social media , Redfearn said at a briefing it “would be irresponsible for me to speculate on a motive.”

The violence broke out around 1:30 p.m., at 13th and Pearl streets on Sunday as crowds of people milled around a pedestrian-only area, Redfearn said.

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