LONDON — Three months after a flurry of letters called for a day of violence and abuse against Muslims, the British police arrested a man on suspicion of making the threats, though it was unclear how many of the letters he was believed to have sent.
The police gave little information about the suspect, saying only that he was 35 and lived in Lincoln, in eastern England. He was arrested on Tuesday by Counter Terrorism Policing North East, aided by the Lincolnshire Police, and the authorities said they had also searched a residence and an office building in the area.
The letters declared April 3 as “Punish a Muslim Day,” and called for offenses ranging from verbal abuse to murder and bombings, assigning a point value to each one. Some contained what was feared to be a toxic substance but turned out to be harmless. The letters went to mosques, community centers, schools and homes across Britain, and even to Muslim members of Parliament, prompting evacuations of some parliamentary offices in Westminster.
The threats drew widespread fear and anger, drawing attention in news outlets and on social media, including in the United States. But the day passed quietly.
Britain has become more ethnically diverse in recent years, but that change, combined with Islamist terrorist attacks, has prompted a backlash in some quarters. The country voted in 2016 to leave the European Union, in part to restrict immigration, and there has been a sharp rise in hate crimes.
For months, there has been speculation that the “Punish a Muslim” letters were sent by multiple people, whether copycats or working together, but the authorities in Britain have not said how many might have been responsible.
The police said the man being held had been arrested on suspicion of sending a threatening communication, soliciting murder and sending a hoax noxious substance.