The Ontario Provincial Police have gone back to court to seek more documents related to the Liberals' $1.1-billion gas plants scandal.

OPP Superintendent Paul Beesley, director of the forces's organized crime enforcement bureau, confirmed to the Star that another search warrant - the third in a 20-month investigation - was executed.

Officers want to examine more emails of former premier Dalton McGuinty's last chief of staff, David Livingston.

Brian Gover, a Toronto lawyer representing Livingston, said Friday he had "no comment" on the police document and the seizure of his client's BlackBerry.

The OPP believe the BlackBerry might contain emails Livingston intentionally kept off government email systems.

The police got a judge's permission to scour the device using evidence recovered from an earlier search. In one of those email exchanges Livingston joked to McGuinty's deputy chief of staff, Laura Miller, that another email wouldn't get special treatment that would scrub messages from the government's files.

The OPP investigation stems from McGuinty's decision to cancel two gas-fired power plants in Oakville and Mississauga before the 2011 election in order to win five local Liberal seats.

McGuinty is not under investigation.

However, his former chief staff is the subject of an OPP breach-of-trust probe.

Police allege Livingston obtained a special computer password that allowed Peter Faist - a private contractor and the spouse of Miller - to erase hard drives.

Neither Faist nor Miller are subjects of the police probe and, like Livingston, have denied any wrongdoing.

The computer scrubbing in early 2013 was conducted in the final days of McGuinty's tenure before Premier Kathleen Wynne took office.

Wynne has repeatedly distanced herself from her predecessor.

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Just before Christmas, after it emerged Faist had been paid $10,000 for his services, the premier ordered the Ontario Liberal Party to repay the money, plus HST, to the treasury.

Auditor general Bonnie Lysyk put the costs of scrapping the two gas plants and relocating them to Napanee and Sarnia at up to $1.1 billion over 20 years.