A 15-year-old girl was allegedly gang-raped by eight youths in a classroom of Purbo Jurain Adarsha High School in the capital.
The incident took place in the early hours of April 29, according to a case filed by the victim on May 1.
Court sources said one of the accused, Swapan, 35, security guard of the school, was arrested soon after the case was filed with Kadamtali Police Station.
Swapan in a confessional statement under section 164 before Metropolitan Magistrate Laskar Sohel Rana have confessed to his involvement in the crime, saying that he had helped the other seven accused enter the school premises in exchange for Tk 1,000, the sources added.
The seven other accused, including prime accused Shaon, 20, are still at large.
Around 6:00pm on April 28, Shaon waylaid the girl as she was returning home in Old Dhaka on a rickshaw after visiting a relative's house, said Kazi Wazed Ali, officer-in-charge of Kadamtali Police Station, quoting the FIR.
Shaon at this stage threatened the girl with dire consequences unless she got off the rickshaw and went with him inside the school nearby.
After she complied with his demand, the security guard, Swapan, confined her to a classroom on the first floor of the school.
Around one and a half hours past midnight, on April 29, Shaon came back and introduced the seven other youths -- Munna, Jalil, Swapan, Mishal, Masud, Sajib and Tanjil alias Tanju -- to her saying that they would all rape her.
Munna then tied her hands and gagged her while all of them took turns to rape her on a bench till 2:00am.
The criminals put the profusely bleeding girl on a CNG-run auto rickshaw around 6:00am and the driver dropped her off on Chairman Bari Road.
The victim then went to her maternal uncle's house nearby, according to the case statement.
She was later taken to One-stop Crisis Centre of Dhaka Medical College Hospital (DMCH) for medical treatment and tests.