Former Victorian treasurer John Lenders faces police interrogation over his involvement in an election rorts scheme, while 16 current Labor MPs have been cleared of criminality.
Mr Lenders, previously named as an architect of the rort, will be "criminally interviewed". An unnamed electorate officer also has questions to answer over the so-called "red shirts" scandal.
Deputy Commissioner Shane Patton on Thursday said the ongoing investigation would take no more than two months, given most of the evidence has already been established.
"That would progress very quickly, moving forward," he told reporters.
Mr Lenders was treasurer from 2007 to 2010 in the Brumby government before his departure from parliament.
Police had good news for Labor with the exoneration of still-serving MPs.
"The fraud and extortion squad have determined no charges will be laid against any of the electorate officers in this matter. No charges will be laid against any of the 16 members of parliament ... as well," Mr Patton said.
He added that all of the politicians involved had been asked but refused to be interviewed by police.
"This is over for MPs. It means MPs, as they always have done, remain focused on delivering for Victorians," Police Minister Lisa Neville told reporters in Ballarat.
Ombudsman Deborah Glass previously found 21 past and present Labor MPs systematically misused public money during the party's successful campaign, with $388,000 in taxpayer funds approved for electorate officers who instead worked as campaign staff.
She also found their actions were "in good faith, depriving no personal benefit".
Senior ministers Lily D'Ambrosio, Jenny Mikakos and Gavin Jennings were among MPs named as breaching the system and exonerated on Thursday.
Police Chief Commissioner Graham Ashton said the investigation "didn't leave any stone unturned", and legal advice resulted in the decision not to charge MPs.
But Opposition Leader Michael O'Brien was stumped by the police decision.
"Any Victorian who rorted money from their workplace would expect to be charged with a crime," he said.
"Ordinary Victorians will be asking themselves whether a Labor party membership doesn't come with a get-out-of-jail-free card."
Labor has already repaid the $388,000.
Australian Associated Press