In this direction, the investigating agency conducted a lie-detector test on the doctor couple’s maid Bharti, sources said. Later in the evening, a team of sleuths went to Dr Anita and Prafful Durani’s house in Sector 53 and took them to CBI headquarters for psycho-analysis.

Sources said they were analysed to check whether their statements corroborate with those given by their household help Rajkumar and Bharti.

On Wednesday, the CBI also questioned Talwars’ driver Umesh once again.

Interestingly, the agency is now also looking at a possible contract-killing angle, and therefore the focus on Umesh, sources said.

The agency had conducted a lie-detector test on Duranis’ domestic help Rajkumar and searched his room on Tuesday.

Talwars’ teenaged daughter Arushi and household help Hemraj were murdered sometime on may 15 night.

About repeated questioning of all the helps, a senior CBI official said, 'They are being questioned to know Krishna’s exact position on the night of murder since his family claims that he was home (on May 15 night). These domestic helps know each other very well, so we are checking all places where Krishna might have gone to locate the murder weapon.

CBI has conducted six lie-detector tests till now: three on Krishna, one on Nupur Talwar, one on Rajkumar, and on Bharti today. The agency has also put Krishna under narco-analysis test.

Since taking over the investigations from Noida police on June 1, the probe agency has also done psycho-assessment of Dr Rajesh Talwar (still in custody), his wife Nupur, their clinic compounder Krishna, associate and family friend Dr Anita Durani, and her help Rajkumar.

CBI officials said these tests have provided clues that have led them to construe Krishna’s involvement. "After getting final reports of these tests we will match the results with statements given to Noida police," the CBI source said.

According to the source, CBI teams have closely analysed call details of Rajkumar, Krishna and Hemraj’s cellphones. The investigators, the source said, believe the three were in touch before the murders, though Rajkumar and Krishna had reportedly stopped meeting soon after the incident.

Under test fire

Lie-detector

Krishna: 3 (also under narco)

Nupur Talwar: 1

Rajkumar: 1

Bharti: 1

Psycho-assessment