Ornge founder and former chief executive officer Chris Mazza is set to speak publicly for the first time on Wednesday about his role at the embattled air ambulance service.

A Speaker's Warrant was issued in May compelling Dr. Mazza to testify at a government committee probing multimillion-dollar contracts and questionable business practices at Ornge. He has been unable to appear until now because he has been under medical care, said someone close to him.

Dr. Mazza has kept a low profile since he went on medical leave last December. He was terminated in February, ending his six-year reign at Ornge and his dream of leveraging the publicly funded "hospital in the air" into a world-class medical transport business.

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Several officials associated with Ornge have already testified at the all-party committee hearings, including former executives, board members, legal advisers and Dr. Mazza's girlfriend, a former associate vice-president at the air ambulance service.

But Dr. Mazza will be the star witness because of the key role he played at Ornge.

He assumed responsibility for Ornge in 2005, after the McGuinty government created a new entity responsible for all aspects of the provincial air ambulance service, including managing contracts with private-sector air carriers to supply helicopters and planes.

Dr. Mazza earned $1.4-million a year, making him one of the province's highest-paid public sector employees.

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He has left behind an organization mired in controversy over a series of private, for-profit ventures that are now part of an Ontario Provincial Police probe.

Ontario's Health Ministry is investigating 13 Ornge-related incidents, including three deaths, to determine whether the care of patients was compromised in the name of profit.

Investigators are also looking into the $148-million Ornge spent on a fleet of helicopters whose medical interiors are rife with problems, making it difficult for paramedics to perform life-saving CPR.

Premier Dalton McGuinty, who was introduced to Dr. Mazza at a Liberal fundraiser back in 2007 by former Ornge legal adviser Alfred Apps, said he is looking forward to the former CEO's testimony.

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"I think it's an opportunity for us to get to the bottom of a lot of things," he told reporters on Tuesday.