The Central Bureau of Investigation on Monday began questioning Rajesh Talwar who was arrested by Uttar Pradesh police in connection with the murder of his daughter Aarushi and a domestic servant.
The agency moved an application before a court in Noida for his extensive questioning.
CBI officials said since the statements of Talwar's wife Nupur, their other domestic help and neighbours have been taken, it is necessary to corroborate them.
The CBI has also taken all documents from Uttar Pradesh police, including the laptop of Talwar and desktop of his daughter for a detailed analysis.
"Our first aim would be to retrieve as much as possible, the data deleted either from the laptop or the desktop," a senior CBI official said.
The Noida court granted permission to the CBI for questioning Talwar, a dentist by profession, who was arrested by the UP police as they claimed that he had killed Aarushi in a fit of rage after he found her with Hemraj in an "objectionable" position.
The UP police also alleged that Talwar had taken Hemraj to the terrace and killed him before doing his daughter to death.
However, his counsel and wife Nupur have denied the allegation. The CBI registered a case on Sunday against unknown persons and formed a 25-member team to probe the conspiracy behind the murder.