Werner Gallmeister, a high-school headmaster here, called the police in January with a worrying message. A 16-year- old student known for his Islamist sympathies had been showing off a smartphone video of an explosive device.
Police already knew the teen. He had been interrogated and suspended from one school after threatening to “break the neck” of a Jewish student. Police in 2015 searched his home. And he was enrolled in a government-sponsored program designed to prevent radical youngsters turning to violence.
Soon after the smartphone stunt, Mr. Gallmeister reported to police that his pupil’s behavior seemed to calm. He was wrong.
Three months later, the teenager, whom German officials and police identify as Yusuf T., allegedly threw a bomb at a Sikh temple in the nearby city of Essen as a wedding was drawing to a close. The Wall Street Journal isn’t using his full name in accordance with German custom. In the attack, three people were injured, one seriously.