Officers have travelled across Ontario and outside Canada to interview more than 50 people since they started the investigation just over a year ago, he told a legislative committee.
They've contacted law enforcement agencies in the United States and Italy and pored through 22,000 pages of documents as well as 500,000 emails, Lewis said.
It's not unusual for such complex cases to take years to complete, he said. Some end with no charges being laid.
"I can't put an end date on it, but I am confident within a year, we'll know whether there will be criminal charges laid," Lewis said.
Ornge, which receives about $150 million from the province, has been under fire for more than a year over sky-high salaries, financial irregularities and allegations of kickbacks.
The head of Finmeccanica, an Italian company linked to Ornge, was arrested in February in connection with an investigation involving bribes in the US$670-million sale of 12 helicopters to the government of India.
The Progressive Conservatives say the deal is very similar to the $144-million deal helicopter-maker AgustaWestland, a subsidiary of Finmeccanica, signed with Ornge for 12 helicopters.
Agusta paid an Ornge spinoff company $6.7 million after it reached the deal, which included a $4.7-million agreement for marketing services.
Ousted Ornge chief executive Chris Mazza testified that the extra fees were not part of a kickback scheme. Agusta has vehemently denied any wrongdoing.
"Based on what we heard in this committee, I can tell you that I would be shocked if criminal charges weren't laid," said Tory Frank Klees.
Lewis said he anticipates OPP investigators will want to go to Italy.
He wouldn't say whether police have spoken to Mazza. But Lewis acknowledged that while Ornge has co-operated fully, there have been some obstacles in the case.
"I know some people have been more co-operative than others," he told reporters outside the committee room.
"There have been some people, as in any investigation, that are reluctant to speak to police. And sometimes that's for nefarious reasons and sometimes it's not."
Ornge's current president and CEO Dr. Andrew McCallum testified earlier that paying out nearly $2 million in bonuses has caused Ontario's troubled air ambulance service to slip into the red.
Bonuses were almost always paid in the past — about 97 per cent of the time — to managers and executives, said McCallum. It's a "major reason" why a federal ajudicator ruled that Ornge must make the payouts.
Ornge promised last year to cancel bonuses to all non-unionized staff. But a group of federally-regulated employees appealed the decision and won.
Ornge will give performance pay to 424 unionized and non-unionized employees this fiscal year — an average of about $4,632 each.
Ornge is now grappling with a $2.5 million deficit, McCallum said.
From now on, the rules will change, he told the committee. Any bonuses for non-unionized staff will depend on whether they achieve certain "personal and corporate goals."
Last August, the all-party committee heard that Mazza received at least $1.4 million in compensation, including bonuses. He also received about $1.2 million in loans in a single year, according to documents tabled with the committee.
Mazza received $500,000 from Ornge Peel in July 2010, $250,000 from Ornge Global and another $450,000 from Ornge Global in July 2011, according to the documents, which also detailed his lavish expenses.
Ornge is seeking $500,000 plus interest from Mazza, alleging he defaulted on a loan that he used to buy a house in west Toronto.
In a statement of claim filed Jan. 22 in a Toronto court, Ornge alleges that Mazza sold the house without telling Ornge, and has "failed or refused" to repay the loan.
Ornge said bankruptcy trustees are pursuing repayment of other loans Mazza received. They've recovered about $600,000 from the sale of Mazza's home, said Ornge spokesman James MacDonald.
A portion of those funds will come back to Ornge once the bankruptcy proceedings are complete, McCallum said.
Auditor General Jim McCarter has criticized the governing Liberals for failing to oversee Ornge, despite giving it $730 million over five years and allowing it to borrow another $300 million.
The Progressive Conservatives complained Wednesday that Ornge is not providing certain documents, such as banking records for Ornge's now-bankrupt, for-profit spinoff companies.
But Health Minister Deb Matthews said they're doing everything they can to comply with the committee's request for information.
"Some 500,000 pages of documents ... have been delivered to the committee," she said in the legislature.
"We also have another 1.5 million pages of documents that are being provided on USB sticks, so Ornge is complying fully and the ministry is as well."