Kolkata/IBNS: The Central Bureau of Investigation is focussing on whether the 31-year-old lady trainee doctor at Kolkata's state-run RG Kar College and Hospital was raped and murdered by one person or was it a gangrape as the clamour demanding justice in the case is growing louder.

The CBI is trying to find out whether accused Sanjoy Roy, the arrested civic volunteer, is the only one who is associated with the rape and murder of the medical student.

As per the autopsy report, 150 mg of semen was found in hymen. Now some doctors suspect medically it was not possible for one man to commit the crime.

The Kolkata Police on Wednesday handed over arrested civic volunteer Sanjoy Roy, who is accused of raping and murdering a trainee doctor at RG Kar Medical College and Hospital, to the Central Bureau of Investigation.

Sanjoy has been handed over to the central probe agency's custody a day after the Calcutta High Court ordered a CBI probe into the incident, which sent shockwaves and triggered huge anger across the country.

The CBI will probe into the case, which has brought the Mamata Banerjee government under the scanner, under court monitoring.

Sanjoy was taken into CBI custody after his medical tests were conducted at the state-run SSKM Hospital.

The 31-year-old medical student was allegedly raped and murdered at the seminar hall of RG Kar Medical College and Hospital, which is located in North Kolkata's Belgachia area, last week.

Though the civic volunteer has been arrested in connection with the case, protesting students, who went for ceasework across the state, suspect more people are involved in the case.