Police were deployed at all four exits of Presidency College on Thursday to prevent entry of unauthorised persons, but an inspection revealed that the ?enemy? lay within ? outsiders lodged in the staff quarters on campus.

?Unauthorised occupants will be driven out of the quarters to revamp security,? Dulal Chakraborty, assistant commissioner of police (central division), asserted on Thursday.

The ?marathon check? on the college compound followed an attempt by an outsider to molest a student on Wednesday morning. A middle-aged man, often seen hanging around with his associates, accosted the student of the sociology department, made obscene gestures and even followed her into class. He fled after being chased by a group of students.

Police, however, are not sure whether the man lived in the staff quarters. ?We cannot say so till we arrest him,? Chakraborty said.

Officers of Jorasanko police station, which oversees security on the campus, said ?ruffians? from areas adjoining the Calcutta Police morgue often took shelter in the staff quarters. ?We may have to interrogate those living in the quarters,? said an officer.

Chief minister Buddhadeb Bhattacharjee, following a briefing by home secretary Prasad Ranjan Roy, is learnt to have expressed concern over the ?unpleasant incident? at his alma mater.

College principal Amitava Chatterjee, on his part, held a second round of talks on Thursday with the students? union and senior teachers to work out a security revamp scheme. All sides agreed that unauthorised persons needed to be driven out of the campus.

?We have urged the college authorities to introduce photo-identity cards for all staff members to ascertain whether outsiders are living in the quarters,? said union general secretary Anirban Saha.

The authorities, he added, will issue a circular on Friday, listing dos and don?ts for students and teachers. ?We will fully back the authorities in tightening security. Entry of outsiders has to be restricted to ensure safety of students and employees.?

Principal Chatterjee also met the headmaster of the adjoining Hare School and discussed the construction of a wall between the two institutions. ?Students of the school and their guardians often loiter around the college,? alleged a student of Presidency.

The All India Democratic Students? Organisation, an affiliate of the SUCI, held a sit-in at the college main gate again on Thursday, demanding a probe into the incident.