The CBI on Friday conducted a lie detector test on Vijay Bhardawaj, who allegedly gunned down controversial Assistant Commissioner of Delhi Police Rajbir Singh.
Bhardawaj, who is at present in judicial custody, has been brought to the capital from Ambala in Haryana, and subjected to the test.
The CBI questionnaire for the lie detector test includes the overseas calls received by him before and after the murder of Rajbir and also the hefty amount of money deposited to his bank account after the crime, sources said.
Bhardawaj, a property dealer, had confessed before media immediately after the March 24 murder that he killed his friend at his Gurgaon office.
The CBI started investigation into the murder after registering a case on June three following a request by the Haryana government for a probe by the premier investigating agency, which was approved by the Department of Personnel on May 27.
The family of Singh, who was part of investigations into several high-profile cases, including attack on Parliament, had demanded a CBI inquiry into the case claiming that "a much bigger conspiracy was behind the killing".
Rajbir's father Mamchand Yadav had said that "it is a case of murder of a highly decorated police official and a high-powered body like the CBI should carry out investigation into it".
His wife too joined the chorus demanding a CBI probe and said, "It's not so easy to kill a top cop. A man like Vijay (Bhardwaj) cannot do this by himself. He is just a property dealer and would not have the courage to kill him unless he was pressurised. The police needs to investigate this aspect."
Singh, who had joined Delhi Police as a Sub-Inspector in 1982, had 56 encounter killings to his name.
But he came under a cloud with questions being raised over his alleged links with the mafia in the national capital region and for a number of "fake encounters".
His career started showing a dip immediately after KK Paul took over as Commissioner of Delhi Police and shunted him out of the Crime Branch following allegations that he was involved in a drug trafficking case.
However, an inquiry by the Delhi Police absolved him of all charges and indicated a well-planned conspiracy to malign his image.