Before Monday’s attack, London’s Finsbury Park Mosque had known two very different histories. The first was one of extremism and hate. Under the notorious Abu Hamza, Finsbury Park was connected to the 2001 shoe bomber who tried to blow up a trans-Atlantic airliner, as well as a 2003 alleged plot to create ricin poison.

Then, everything changed. Mr. Hamza was arrested, and new leadership vowed to preach tolerance. By 2014, the mosque became the third faith organization to receive a prestigious British award for community service, the Visible Quality Mark.

“We feel a strong sense of responsibility,” the mosque’s chairman told The Independent. “We think we should be role models to other mosques and other faith places, to deal with extremism....”

On Monday, a man driving a van injured 10 Muslims leaving Ramadan services at Finsbury Park, killing one. Those who survived apprehended the man, then formed a protective circle around him so no one would take revenge. Often, the question is asked: What are Muslims doing to counter extremism in Islam? The irony of Monday’s attack is that a radicalized Westerner brought to light a powerful answer.