The Central Bureau of Investigation on Wednesday subjected Nupur Talwar, the dentist mother of slain teenager Aarushi, to a lie-detector test at its headquarters in New Delhi.
The CBI put Nupur through a seven-hour lie-detector test.
"The duration of the test was about seven hours and several questions were asked as her first test proved inconclusive," a CBI official said.
Nupur's lie-detector test was earlier scheduled for Tuesday. But it was rescheduled for Wednesday after Nupur arrived late at the headquarters.
Aarushi, 14, was found murdered in her parents' Jal Vayu Vihar apartment in suburban Noida on May 16. The police initially named the family domestic help Hemraj as the prime suspect, but backtracked when his body was found on the terrace of the apartment the next day.
The police arrested Rajesh Talwar, a dentist, on May 23 saying he had killed the two as he was opposed to the close ties between Aarushi and Hemraj and also because she knew about his extra-marital relationship with a colleague, Anita Durani.
The agency arrested Krishna, the compounder of Rajesh Talwar, on June 13 and said he had confessed to his involvement in the murders.
The CBI, which took over the case June 1, has not yet been able to locate the weapon used in the double murders or establish the motive for the crime.
On Monday, the CBI was given four more days' custody of Krishna. The probe agency had earlier claimed to have recovered a khukri (curved short knife) from Krishna's room. The knife has been sent for forensic examination.
According to sources, forensic tests on the khukri have ruled out its use in the crime.