Three out of the four accused arrested in connection with the alleged gangrape of a student at a city-based law college had pre-planned the assault, a police officer said on Monday.

Sleuths of the nine-member Special Investigation Team (SIT) probing the incident also found that the three accused — Monojit Mishra, Pratim Mukherjee and Zaid Ahmed —  had a history of sexually harassing female students of the college. The fourth accused is the college’s security guard.

According to the officer, the trio would record such episodes on their mobile phones and later use the footage to blackmail the victims. “The entire matter was premeditated. The trio had been plotting for several days to carry out this torture on the victim,” the police officer said.