The Himachal Pradesh police had arrested Ashish Chauhan alias Ashu (29), a resident of Sharaal village in Mahasu area of Kotkhai; Rajender Singh alias Raju (32), a driver; Subash Singh Bisht (42) and Deepak alias Deepu (29), both residents of Pauri Garwal; Suraj Singh (29) and Lok Jung alias Chotu (19), both hailing from Nepal.
Among these, Suraj Singh was found dead in police custody in which a separate case has been registered by the CBI.
The sources the said agency had moved a plea in a Shimla court seeking permission to conduct polygraph test on these arrested suspects which has been granted after taking their consent.
A 16-year-old girl had gone missing after school hours on July 4 from Haliala forest in Kotkhai area of Shimla district.
The DGP constituted an SIT headed by an officer of IG rank which arrested six persons.
The case was handed over to the CBI by the Himachal Pradesh High Court on July 19 on the state government's plea amid public outburst against the state police. The CBI filed two FIRs on July 22.