McGuinty released a brief statement late Friday afternoon saying that the victims' families "have raised important questions that deserve to be answered.
"We have an obligation to do whatever we can to prevent similar tragedies and respond in the best way possible when they do happen," the statement said.
"Details about the inquiry will be announced later."
Provincial NDP Leader Andrea Horwath welcomed the announcement.
“We owe it to the people who lost their lives, the people of Elliot Lake and all Canadians to take an independent look at everything that led to this disaster and everything that happened after," she said in a statement. "I look forward to getting the answers people deserve.”
Previous visits by government inspectors
On Friday, the Ontario Ministry of Labour released six field reports on the mall dating from October 2009 to January 2012.
The ministry is responsible for the health of safety of workers in the province. It does spot checks and workplace safety inspections, but also responds to complaints. The most recent report detailed a visit by ministry staff investigating a complaint about the roof.
"Top floor of most of the mall is outdoor parking to accommodate the needs of the mall & its tenants," the background section of the report says. "Leaks have occurred in the past despite a snow removal program which involves and includes rubber blades."
The report goes on to say that an "Ongoing maintenance program is in place to patch leaks and attempt to identify source location."
The building's owners, Eastwood Mall, "are evaluating their options and will be dealing with this problem on a permanent basis spring/summer 2012," the report says.
The ministry issued no orders after investigating the complaint, because there were no violations under the Occupational Health and Safety Act, a ministry spokesman said. It's not clear when the complaint was filed, or who filed it.
Victims officially identified
The bodies of Lucie Aylwin, 37, and Doloris Perizzolo, 70, were pulled Wednesday from the rubble of the mall during an intense search effort involving special heavy machinery that carefully dismantled parts of the building.
Both victims were officially identified Friday by Ontario's Office of the Chief Coroner, though their deaths had been widely reported days earlier and McGuinty had already offered his condolences to their families.
The mall's roof-top parking lot caved in Saturday, sending debris crashing through two storeys of the building.
Local residents have since complained that the building was in shabby condition before the cave-in and have questioned the speed at which rescuers tried to reach those trapped in the rubble.
A police officer, a firefighter and an engineer will be sifting through debris at the mall to collect information that will aid the chief coroner and the Ministry of Labour in their investigations, officials said.
An engineer with the ministry will try to determine the safety of the building, after emergency teams spent days dismantling sections of it in order to reach the two victims killed in the collapse, said Dan Hefkey, Ontario's commissioner of community safety.
"At that point, what he's going to do is, he's focusing on the how and the why," Hefkey said.
"So are there other structural issues further through the building, as well as figuring out at that site in question where we recovered the two bodies exactly the how and the why there."
The engineer will be able to give that information to the mall's owner, who will decide if the building will be torn down, Hefkey said.
Tenants complained of leaks
CBC's John Lancaster and John Nicol reported Friday that the building's woes date back several years, and that a mall employee had been badly injured in 2007 by a falling piece of drain pipe that had been connected to the roof.
Some of the shopping centre's main "anchor" stores were forced to use tarps to protect against leaks.
During that period, key tenants, such as Zellers, "were making louder and more frequent complaints to mall ownership that they were going to pull out [of their leases], unless these leaky roof systems were corrected," Lancaster said.
On Thursday, a representative of the mall's owner faced tough questions and shouting from furious local residents.
"My family was in the mall when it collapsed. If I had thought there was any danger, I certainly would not have put my family in harm's way," lawyer Antoine-René Fabris told an angry resident, who accused the Algo Centre owner of knowingly allowing the mall to continue operating, despite the building's apparently questionable structural integrity.
"Madam, I'm a person of Elliot Lake, too," an emotional Fabris said, responding to a community member who accused the mall's owner of viewing local residents "as dollar signs" rather than lives.
Mall's owner facing class-action proceedings
Fabris spoke on behalf of Bob Nazarian, the mall's owner, and said the owner would return to the scene as soon as the mall is released back into his possession by the authorities. He confirmed that a notice of class-action proceedings has been delivered to Nazarian, adding that the owner's family has received a number of death threats. He didn't elaborate.
In an interview with CBC News on Friday, former Elliot Lake mayor George Farkouh, who served until 2006, said the angry reaction from residents was understandable.
"We're all hoping in Elliot Lake that we'll find the cause of this through the proper investigations with the OPP and Ministry of Labour and other agencies," Farkouh said. "This should never happen in a province or a city like Elliot Lake or in Canada, and we should learn from this and avoid this ever happening again."
During his nearly 20 years as mayor, Farkouh added, there was little reason to predict such an immense tragedy could happen at the mall.
"There was the usual leaky roof. However, we put our library in there about 22 years ago. We had full confidence in the mall then," he said.
A statement issued Thursday said the OPP's criminal investigation branch was conducting a death investigation into the mall collapse, along with members of the Office of the Chief Coroner.Suggest a correction