During the questioning on Thursday, IB sleuths asked Chandra, who was then Member (Investigations) in the CBDT, why private detectives were called before informing the IB to inspect the plated "bugs" in the Ministry of Finance, official sources said.
When contacted, Chandra denied that he has been quizzed by anyone, saying at the time of reported "bugging" he was not the chairman of CBDT and he had no role in hiring private detectives.
An inquiry is also on to find out the name of the private detective agency which carried out the debugging exercise in the Ministry of Finance.
"It is not a formal inquiry but discreetly the investigators are trying to find out the name and the findings of that agency," the sources said.
After the detection of "planted adhesives" in 16 key locations in the offices of the Finance Minister, his advisor Omita Paul, his private secretary Manoj Pant and two conference rooms, Mukherjee wrote a letter to Prime Minister Manmohan Singh asking him to order a "secret inquiry" into what he called "serious breach of security" in his office.
Before the IB was asked by the Prime Minister to look into the matter, private detectives were called to conduct an "electronic sweep" on the Ministry's chambers.
Mukherjee last week had said that during its inquiry, the IB has found "nothing".