Former Uttar Pradesh minister Amarmani Tripathi, prime accused in the Madhumita Shukla murder case, underwent a lie-detector test on Monday, the Central Bureau of Investigation said.

Tripathi gave in writing to the CBI on Sunday evening his acceptance to undergo the test.

The polygraph test, which continued for nearly three hours, will help the sleuths in figuring out if Tripathi had lied while giving his statement.

Tripathi was first explained the significance of the polygraph test and the method with which it works before the questioning by senior officials of the CBI began, sources said.

The test is being conducted at the Centre for Forensic and Scientific Laboratory located within the headquarters of the agency.

Tripathi was arrested on September 21 at Lucknow and later brought to Delhi.

The Uttar Pradesh legislator had been complaining of one health problem or the other during his custody after which the agency decided to keep him in its ground floor located lockup over the weekend.

Tripathi has been confronted with the servant of Madhumita, Desraj, who is presently under protection of the agency.

The CBI was also looking for the wife of Tripathi, Madhumani, and had carried out searches at various places since the past few days.