Shahidul Alam says he was tortured.

The last time the acclaimed Bangladeshi photographer Shahidul Alam had a major run-in with the police, it was for a 2010 project documenting official torture and death squads, which led the Dhaka police to besiege and shut down his gallery and provoked national protests on his behalf.

This time, he was picked up in connection with protests that have roiled Bangladesh for the past two weeks, mostly by high school students angered by the deaths of two students killed by a speeding bus.

At least 20 police officers raided Mr. Alam’s home on Sunday, hours after he posted a video on Facebook saying that he had been beaten up by pro-government thugs