Police have arrested a man in connection with the killing of a 17-year-old student in the capital's Kafrul area.

The arrestee was identified as Md Abdullah Al Mamun alias Mamun Sarkar, 24.

According to police, Mamun developed a friendship with Md Rakibul Islam, 17, after meeting him online a few months ago. On September 16, Mamun allegedly called Rakib over WhatsApp and took him to his residence in Shukrabad after asking him to come to the area in front of Shewrapara Metro Rail Station.

He allegedly held Rakib hostage and demanded Tk 15 lakh in ransom from his family. At one point, a scuffle took place between them, during which Mamun allegedly twisted Rakib's neck, causing his death.

Briefing reporters at the DMP Media Centre on Minto Road on Wednesday, Dhaka Metropolitan Police Joint Commissioner (Crime Prevention-North) Md Mahidul Islam disclosed the details.

He said Rakib lived at a mess in East Shewrapara and had enrolled at a coaching centre in Farmgate to prepare for university admission after completing his HSC examination.

At around 4pm on September 16, someone called Rakib over WhatsApp and took him outside the residence. He did not return home afterwards, the official said.

Later, Rakib's family received phone calls and online messages demanding Tk 15 lakh as ransom, with threats to kill him if the money was not paid.

Hoping to secure Rakib's release, his family paid a total of Tk 4 lakh through four bKash and three Nagad numbers at different times, Mahidul said.

Rakib's elder brother Zohurul Islam Jibon initially filed a general diary over his disappearance with Kafrul Police Station and later filed a case over his abduction and the ransom demand, he said.

During the investigation, police identified Mamun as the user of two WhatsApp numbers used to demand the ransom, the joint commissioner said.

Mamun was arrested at around 6pm on Monday from the Shukrabad bus stand area under Sher-e-Bangla Nagar Police Station.

According to information obtained during interrogation, after killing Rakib, Mamun put the body inside a carton, wrapped it with tape and took it by autorickshaw to Gabtoli bus stand.

He then travelled by bus and other vehicles to Dimla in Nilphamari and on September 17 buried the body, along with the carton, in a pit in a betel-nut grove in front of his house.

With the assistance of Dimla Police, Rakib's body was recovered from the spot shown by Mamun at around 3:30pm on Tuesday, Mahidul said.

Rakib's elder brother Jibon later identified the body. It was sent to the morgue of Nilphamari Modern Sadar Hospital for autopsy.

Police also recovered Tk 50,000 in cash from Mamun, allegedly from the ransom money.

Investigation is continuing to determine whether anyone else was involved in the killing and to examine the ransom money transactions and other aspects of the incident, Mahidul said.