The body of Suraj was kept in a local hospital, where the autopsy was performed by the AIIMS experts, CBI sources said today.
They also spoke to the doctors who had carried out the first post-mortem.
A team of forensic experts drawn from the CBI, Central Forensic Science Laboratory in Delhi also visited the scene of crime, where the rape and murder is suspected to have taken place, they said.
The team questioned the maternal uncle of the victim. They also questioned some other persons. They would meet parents of the girl tomorrow and also question Suraj's wife.
The agency has urged people to share information about the crime on mobile numbers 8219885920, 8219893590. The rape case had triggered widespread protest in Shimla with the state government on the defensive ahead of the upcoming assembly polls in the state.
The CBI took over the investigation on the direction of Himachal Pradesh High Court.
"It was alleged that a minor girl had gone to school on July 5, 2017 but did not return home. Her body was found in the morning of July 6 from nearby forest area."
"On a complaint lodged by her father with Police Station Kotkhai, Distt. Shimla, the FIR was registered against unknown persons," CBI spokesperson R.K. Gaur had said after the registration of FIR last week.
Local police, which was probing this case, had arrested six accused so far out of which one had died under mysterious circumstances in police custody for which a separate case was registered by the CBI.
The custody of the remaining five accused has also been handed over to the CBI.