CBI officers on Thursday visited the residence of the doctor who was raped and murdered at a Kolkata hospital, and spoke to her parents as a part of their investigation, an official said.

The investigators took note of the time they received the call from the hospital, informing them about the death of their daughter, he said.

The officers also asked them about their daughter's friends, and whether she complained of any problems at the state-run RG Kar Medical College and Hospital where she was a postgraduate trainee doctor, he added.

"It was difficult to speak to a couple who have lost their daughter in such a manner," the officer said.

The CBI also interrogated five doctors of the hospital, its former medical superintendent-cum-vice-principal (MSVP), principal and the head of the Chest Department where the victim's body was found, he said.

The CBI also spoke to the officer-in-charge of the Tala police station, under the jurisdiction of which the hospital is located.

The investigators have sought details of Civic Volunteer Sanjay Roy's call detail record and mobile tower location, among others. He was arrested after the victim's body was found on Friday.

"We are also looking into data consumed by his mobile to ascertain whether he made any video or internet voice calls," the officer said.

A CBI team also visited the hospital during the day, and spoke to intern doctors, nurses and others present there on the fateful night, he said.

The CBI took over the investigation into the case from the Kolkata Police on the direction of the high court.

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