As forensic experts scoured the mill compound for more evidence, the accused were subjected to a Layered Voice Analysis (LVA) test, which is designed for truth verification and detection of deceit.
LVA helps measure the emotional content of human speech, captured live or extracted from recorded audio.
During interrogation, the accused admitted to having raped a ragpicker and a sex worker on separate occasions a few months back, said a crime branch official privy to the probe.
"Also, there appears to be a molestation of a woman, who had come to the defunct mill with her partner," the official said, adding that such incidents as could have occurred over the last six months were being verified.
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Speaking on condition of anonymity, the officer said that they have identified another key witness in the gangrape of the 23-year-old photojournalist.
The victim, an intern with an English magazine, was allegedly raped by the five accused when she had gone on an assignment to the desolate Shakti Mills premises on August 22 accompanied by a male colleague. The colleague is a prime witness in the case.
The officer said that when Salim made a phone call to Kasim on the day of the crime, asking him to immediately reach Shakti Mills, the latter was present in a shanty with Chand, Siraj and one more person.
"That person has been found and made a witness in the case," he said.
Earlier today, two teams from the Central Forensic Science Laboratory, Delhi, and Gujarat Forensic Science Laboratory thoroughly examined the crime scene for nearly three hours to gather evidence for a watertight case against the accused.