TORONTO -- Provincial police say computer experts still cannot determine when 20 of 24 computer hard drives in the Ontario premier's office were accessed with a special password which could have allowed files to be erased.

The police are investigating the deletion of emails related to the Liberals' decisions to cancel two gas plants prior to the 2011 election at a cost of $1.1 billion dollars.

Last month, provincial police seized 24 computer hard drives that had been removed from the premier's office as part of their investigation.

Det. Const. Andre Duval told the justice committee today that the government's Cyber Security Branch had only been able to determine when four of the 24 had been accessed with a special password.

The dates are important because the Opposition says the date range in a requested search warrant goes past Kathleen Wynne's swearing in as premier but Wynne denies any files were accessed after she took over from Dalton McGuinty.

Duval testified the police investigation so far has focused only on McGuinty's former chief of staff, David Livingston, and said Livingston and three others from McGuinty's office all refused to co-operate with the investigation.