Police on Sunday arrested four youths for allegedly conspiring to hurl a crude bomb on the terrace of Free India High School in Titagarh, North 24-Parganas, on Saturday.

Police recovered 10 bombs from the residence of one of the youths, similar to the one that was hurled on the terrace of the school on Saturday from the rooftop of an adjacent building.

All the four accused — Md Aryan, Sadique, Bablu and Md Rehan — were picked up from their respective homes during the early hours of Sunday. Barrackpore police commissioner Alok Rajoria told reporters that the bomb was hurled by one of the youths for “personal reasons” from the rooftop of a six-storey building adjacent to the school, and police traced their activities from the CCTV footage.

Sources in Titagarh police indicated that the bomb was hurled by one of the accused youths to “avenge” rejection by his girlfriend. “They targeted a student of the school who developed a relationship with the youth’s former girlfriend,” a police source said.

Three of the four accused are former students of Free India High School who hatched the plan to target the specific student. The fourth accused backed the trio. After preliminary interrogations, police recovered 10 similar bombs from the home of Rehan. Police commissioner Alok Rajoria refused to disclose the identity of the youth who actually hurled the bomb.

“The investigation is at a very early stage and the person who hurled the bomb is yet to be conclusively ascertained,” Rajoria told reporters.

The four accused were produced before a court in Barrackpore on Sunday and were ordered 14 days in police custody.“They have confessed to the crime. But we needed to interrogate them in detail to know the actual motive behind the attack", the police commissioner said.

On Saturday, a crude bomb exploded on the terrace of the Free India School in Titagarh, unleashing panic among students and teachers. No student was injured in the explosion that occurred at 12.15pm, averting a major accident since all the students were inside classrooms during the time of the blast. An investigating team led by DC (Central) Aashis Maurya was formed. They reportedly cracked the case after scanning CCTV footage.

“From the start, it was clear to us that the bomb was neither hidden on the terrace nor thrown (at the school terrace) from the ground…. So we spotted some buildings nearby that are higher than the school building. We scanned CCTV footage and spotted the movements of the four accused youths,” a police officer said.