Milon Hossain, a teacher in Piyar Ali School and College who was close to Gulshan cafe attacker Shafiqul Islam Ujjal, was held on Saturday night at Ashulia here, police said.
Milon, who earlier worked at Madbar Memorial School in Ashulia, had helped Ujjal get a job as a teacher of the school, a police official was quoted as saying by the bdnews.
He was produced before a court that granted police five days to grill him in custody.
He had left home six months before the attack, his family had said.
Ujjal had told them that he would go to Tabligh Jamaat's 'Chilla', a 40-day travel from one mosque to another to attend lectures and call people to prayers.