CBI sources said they have sent the soiled slippers for forensic analysis hoping they may provide some clue to the crime.
They said a variety of material having evidenciary value like hair, nail, blood, soil etc can be collected from personal belongings of the victim which can help in piecing together the missing clue to solve the crime.
The sources said although they are not doubting the intentions of the family members they are not cooperating enough in the investigations.
Earlier also, the mobile phone of the victim was not provided to CBI officers. When the agency had put pressure, the family provided the phone in broken condition.
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During the examination of the family members, including the fathers of the victims, CBI found a series of loopholes making the investigation difficult.
The two cousins, aged 14 and 15, went missing from their house on the night of May 27 and their bodies were found hanging from a tree in the village in Ushait area the next day. The incident had sparked a nationwide outrage.
The agency is awaiting the results of the polygraph test after which a decision on further tests will be taken.