Iqbal Shakhawat Ovi, a second-year student of electrical and electronic engineering (EEE) was detained from the capital's Hazaribagh on Wednesday.
"Ovi is a friend of Abrar's. They were studying the same subjects in the same batch," said the DB's Additional Deputy Commissioner Arafat Lenin.
Ovi is not among the 19 implicated in the case filed by Abrar's father said Arafat. "We are holding him for interrogation."
The body of Abrar, a second-year student of electrical and electronic engineering at the Bangladesh University of Engineering and Technology or BUET, was found on the staircase of his hall if residence in the early hours of Monday.
He was called up from his room at 7:30pm on Sunday, said police, quoting the students of the hall.
An autopsy at Dhaka Medical College Hospital subsequently revealed that Abrar was bludgeoned with blunt objects.