17-year-old Md Israfil and 15-year-old Robeya Khatun were married about eight months ago
The 'assailant', 12th grader Chan Mahmud, was detained after the hacking on the premises of Alauddin Siddiqui College on Monday, Kalihati Police Station OC Khandaker Md Akheruzzaman said.
The OC, quoting witnesses, said Mahmud hacked Al Amin of the same grade on Monday morning after the latter and his accomplices vandalised Mahmud's motorcycle on Sunday.
"The locals caught Mahmud while he was hacking Al Amin," he said.
Al Amin was taken to Kalihati Upazila Health Complex where he was pronounced dead.
The OC said police were deployed at the college as a security precaution.