Dellen Millard, the young heir to an Ontario aviation business, has been charged with two more counts of first-degree murder in relation to the deaths of his father and a friend.

Mr. Millard, 28, was charged with killing Tim Bosma last spring after the Ancaster, Ont., father went missing while taking two strangers on a test drive of his pickup truck.

Ontario Provincial Police and Toronto Police confirmed on Thursday that Mr. Millard is now also facing murder charges in the deaths of Wayne Millard and Laura Babcock.

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Mr. Millard's friend Mark Smich, 26, who was already charged in Mr. Bosma's death, now faces an additional count of first-degree murder in relation to Ms. Babcock.

Mr. Millard's girlfriend, Christina Noudga, 21, has been charged with accessory after the fact in Mr. Bosma's death.

Mr. Millard's grandfather founded the Millardair airline, which his father transformed into an aircraft maintenance business. Dellen took over the company and a multimillion-dollar hangar in Waterloo, Ont., after his father died on Nov. 29, 2012.

Wayne Millard's death was initially deemed a suicide, but police began reinvestigating after Dellen was charged in Mr. Bosma's death.

Mr. Bosma's charred remains were found on Mr. Millard's 100-acre farm outside Kitchener, Ont. Investigators seized a portable livestock incinerator from the property.

Ms. Babcock's mother, Linda, told The Globe and Mail that she cried when police officers arrived at her home Thursday morning to give her the news of the charges.

Police have so far not announced whether they recovered Ms. Babcock's remains, leading her mother to believe that there's still a chance of finding her. Laura Babcock went missing in early July, 2012.

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"I still am hopeful," she said. "They've just been charged so there's always still a chance."

After the news broke, messages of condolence poured onto a Facebook group devoted to finding Ms. Babcock, a bubbly University of Toronto graduate.

Ms. Babcock, a long-time friend of Mr. Millard's, phoned Mr. Millard several times before she disappeared. The pair had begun a sexual relationship in the first half of 2012 while Mr. Millard had a girlfriend, Shawn Lerner, Ms. Babcock's ex-boyfriend and close friend, previously told The Globe. Mr. Millard later told Mr. Lerner that Ms. Babcock had been asking him for drugs and a place to stay, which Mr. Millard said he declined.

Police have said Ms. Babcock had begun working in the sex trade.

The new charges come several months after detectives found "linkages" in the Bosma, Babcock and Wayne Millard cases and combined the investigations into a multijurisdictional probe headed by senior Ontario Provincial Police Detective Inspector Dave Hillman. The province's serial predator crime investigations co-ordinator was also brought in.

Police searched Mr. Millard's farm outside Kitchener several times, including in September, when the head of Toronto Police's homicide's squad, Staff Inspector Greg McLane, said objects were seized from the property that would be sent for forensic examination.