Sources said investigators are filing a closure report soon following probe into a complaint filed by Bhushan that the CD was fabricated. A case under section 469 of Indian Penal Code (forgery for the purpose of harming reputation) was registered in mid-April.
They said Amar Singh has told police that the voice in the tapes were his and there was "no tampering" of the audio tapes.
The CD was circulated to media houses in April after a fast by Anna Hazare for a strong Lokpal. Hazare's close associate Bhushan was named the co-chair of the joint committee to draft Lokpal Bill.
Bhushan had alleged that the CD was a "cut and paste job" to discredit the civil society campaign.
In the CD, Bhushan is allegedly telling Mulayam Singh and Amar Singh that his lawyer-son Prashant can "manage a judge".
Reacting to the development, Prashant Bhushan told PTI that it appears that some police officials, forensic agency officials, some in government and others have entered into a criminal conspiracy.
"What are they saying about report of CFSL, Chandigarh?" he asked.
The first forensic examination conducted by Delhi Police at CFSL, New Delhi refuted Bhushan's claims that it was doctored triggering demands for his resignation from the joint committee to draft Lokpal Bill.
"There is continuity in the conversation...Recorded conversation is in continuity, no abrupt change in speech signal has been detected," the report made by CFSL, Delhi, said.
However, police had not made public the contents of the second forensic examination conducted at CFSL, Chandigarh.
A forensic test at a Hyderabad-based private lab, Truth Labs, by Bhushan claimed that the disc was "doctored".
The Bhushans had in April got the forensic analysis of CD done by US expert George Papcun and Truth Labs and claimed that the disc has "multiple gaps and signs of electronic editing at very very critical places".
Bhushan had alleged this showed a "very very ominous conspiracy with the blessings of many many powerful people including corporates and politicians" to derail judicial proceedings.
He had claimed that "virtually all portions" of the conversations of Yadav in the CD have been "bodily lifted" from the 2006 tapes, which have purported conversations of Amar Singh with various personalities and submitted to Supreme Court by him.
The CD was circulated two days before the first meeting of the joint committee to draft Lokpal Bill on April 16.
After Shanti Bhushan approached police, a case under section 469 of Indian Penal Code (forgery for the purpose of harming reputation) was registered and the CDs were sent for examination.