Kolkata: Police on Saturday arrested a security guard from South Calcutta Law College in connection with the alleged rape of a first-year student earlier this week, bringing the total number of arrests in the case to four.

The assault, reportedly carried out by an alumnus and two current students, is said to have occurred inside the guard’s room on the college premises on the evening of 25 June. The three prime accused were arrested on Thursday.

According to investigating officers, the security guard--initially detained for questioning--was taken into custody after his responses were found to be inconsistent and CCTV footage confirmed his presence at the time of the incident.

“He failed to carry out his duty,” a senior officer said, adding that police are trying to ascertain whether he was alone on duty that evening. “His behaviour raises questions--why he left his post, on whose instructions, and why he did not act to prevent the crime. His inaction amounts to a form of complicity.”

The 24-year-old victim, in her complaint, stated that the guard failed to help her when the assault occurred. She had gone to the college to submit a form for an examination but was reportedly coerced into staying in the students’ union room.

It is alleged that the alumnus, who is also a criminal lawyer and a contractual non-teaching staff of the college, actually raped her after she turned down a marriage proposal from him, while two existing students stood guard and made a video recording of the act on their mobile phones.

The torture, the victim alleged, started around 7.30 pm and went on till well past 10.30 pm.

These three people were arrested on Thursday.