Jeff Ayotte says the Ontario MP, formerly a member of the Conservative caucus, wants to clear his name of allegations he knowingly exceeded election spending limits.
"His instructions to me are to move this to trial as quickly as possible, so he can at long last exonerate himself," Ayotte said Friday.
Del Mastro faces four charges under the Canada Elections Act linked to a $21,000 personal cheque he paid to an Ottawa political consultant before the 2008 campaign.
He resigned from the Conservative caucus shortly after the charges were laid Thursday.
The Commissioner of Canada Elections alleges that Del Mastro and his former financial agent Richard McCarthy exceeded campaign spending limits, submitted false or misleading paperwork and failed to declare the $21,000 expense on the return.
Del Mastro also faces a separate charge of exceeding the individual spending limit by allegedly contributing to his own campaign.
Ayotte says while the Commissioner of Canada Elections case will be first heard Nov. 7 in Peterborough, Ont., a trial likely won't take place until next spring.
The lawyer would not go into the particulars of Del Mastro's defence, but in the past the MP has said the money was not spent on a campaign expense.
He is the fifth member of the Conservative caucus to resign this year.
Senators Mike Duffy and Pamela Wallin resigned over housing and travel expense irregularities. Senator Patrick Brazeau left caucus when he was charged with assault and sexual assault.
Former cabinet minister Peter Penashue resigned as an MP after it was revealed he submitted ineligible campaign expenses, and lost his seat in the ensuing byelection.
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