CBI sources said the clothes and a few other personal belongings of the victims were collected by the agency from the family members on the suggestion of the three-member panel of the forensic experts accompanying it.
Vaginal swabs collected by local doctors have also been seized by the agency, which will soon be sent to the Centre for DNA Fingerprinting and Diagnostics in Hyderabad for DNA analysis, the sources said.
They said the Centre is likely to give a report within a week to the agency.
The team of CBI and Medical Board had visited the family of the two rape victims as it could not conduct a fresh autopsy because the rising water level of the Ganges river inundated the graves of the two sisters.
The sources said the analysis of DNA collected from the personal belongings will be used to identify the accused.
They said swabs can be stored for long and the results may not be affected.
In the technique, the forensic experts first try to differentiate male and female cells in the swab using a variety of chemicals and later from the male cells they identify the DNA in sperm cells. By doing the cross-matching with the suspects, the forensic experts can identify the accused.
In the absence of any fresh autopsy, the medical board has to rely on DNA analysis which can be recovered from the personal belongings of the victims.
The assailants then got into the car in which they came and drove off.