Less than two hours after mourners gathered in Southport, England, on Tuesday evening to honor three children killed in a brutal stabbing attack, hundreds of rioters flooded the streets of the already traumatized town.

More than 50 police officers were injured in the ensuing violence, as demonstrators threw bricks at a mosque, attacked the police, set cars on fire and damaged a convenience store.

Although some details of the unrest remain opaque, one thing is clear, according to the police, lawmakers and experts in online extremism: Disinformation and far-right agitators fueled the violence.

Supporters of the English Defence League, an extremist anti-Islam organization, were part of a large group that attacked a mosque in Southport around 7.45 p.m., according to a statement from the Merseyside Police Service, which covers the region.

The targeting of the mosque, and the subsequent riot, came after false rumors circulated on social media on Monday, soon after news emerged that a man had stabbed multiple children and two adults at a Taylor Swift-themed dance class.

The rapid spread of misinformation about the attacker’s identity left the authorities fighting a two-pronged battle on Tuesday: one on the streets of Southport, where the police were pelted with bricks and other objects, and another online, where lawmakers, local officials and the police seemed powerless to halt viral falsehoods.