Highly placed sources in the CBI said this was the first brain-mapping test on the doctor couple ever since 14-year-old Arushi and their domestic help Hemraj were murdered on the intervening night of May 15 and 16 in 2008 at their residence in Noida. Polygraph and psycho-analysis tests had been done on the two last year. The sources said the couple was taken to Bangalore too as part of the investigations, but it was not confirmed if a narco-analysis test was also conducted on them.

The CBI had earlier given a clean chit to Dr Rajesh Talwar in the case.

The agency was also criticised for not being able to prove charges against three suspects — Krishna, Rajkumar and Vijay Mandal.

When asked about the brain-mapping, CBI spokesperson Harsh Bhal said: “It is a sensitive case and we follow a policy of not sharing details of investigation.”

The sources, however, said after the agency could not find the murder weapon and the mobile phones of Arushi and Hemraj, and was also unable to file a chargesheet on September 10, 2008, the new team constituted in the case decided to revisit the investigation. The decision on a brain-mapping test on the Talwars was then taken and quietly implemented, they added.

Dr Nupur Talwar, however, denied this on Thursday.

“There is nothing like that. I don’t want to comment on anything,” she said.