“It’s a sad and unfortunate incident. One has been remanded and another has been arrested. The rest will be arrested soon. None will be spared,” he told reporters at his office on Monday.
Samiul Islam Rajan was beaten to death on July 8 morning after being accused of stealing a rickshaw van at Kumargaon of Sylhet Sadar Upazila.
One of those involved in the atrocity had filmed the shocking footage and released it on a social networking site.
The 28-minute video clip created a furore on the social media after it went viral on the internet.
Locals caught one Muhith Alam and handed him over to police after the murder when he was trying to take away the body in a microbus.
On Monday, police arrested another over the incident.
The autopsy report says that the 13-year-old died of brain haemorrhage after sustaining head injuries. Over 60 injury marks were found on the body.