The alleged attack had triggered a tussle between the Delhi government and its bureaucrats.

The time displayed on the CCTV cameras at Chief Minister Arvind Kejriwal's residence on the night of the alleged attack on Chief Secretary Anshu Prakash was nearly 40 minutes behind the actual time, a forensic report has confirmed, ahead of the filing of the chargesheet in the case.

A senior police officer privy to the investigation said the forensic report was received earlier this week.

The report does not mention whether the cameras were tampered with or the clock was altered around the time of the alleged attack on Mr Prakash by AAP MLAs or it was set like this.

On February 23, a police team examined the CCTV system installed at Mr Kejriwal's official residence in Civil Lines area and seized the hard disk connected to the system for investigation.

Fourteen of the CCTV cameras were running while seven did not function. It was found that there was a time lag of 40.43 minutes with respect to the time of the alleged attack, the police had said and now the forensic report has confirmed.

The Delhi Police is expected to file a chargesheet in the case soon.

"We are at an advanced stage of investigation and the chargesheet is being prepared," the officer said without elaborating.

Chief Secretary Prakash was allegedly attacked during a meeting at Mr Kejriwal's official residence on February 19. The police said Mr Kejriwal was present when the attack happened.

They have questioned Mr Kejriwal, Deputy Chief Minister Manish Sisodia and 11 AAP lawmakers present at the meeting. Mr Kejriwal's former advisor VK Jain was also present there.

Two AAP lawmakers - Amantullah Khan and Prakash Jarwal - were arrested in the case; Mr Jain was questioned by the police.

The alleged attack on Mr Prakash had triggered a bitter tussle between the Delhi government and its bureaucrats. The government had accused the IAS officers, who had protested the alleged attack on Mr Prakash, of boycotting meetings with Delhi ministers. The IAS officers have denied the accusation.