As they prepare for a high-profile memorial service on Thursday, relatives of Barry and Honey Sherman want to pursue an investigation independent of the continuing police probe into the Toronto couple's mysterious deaths.

And one of the country's most prominent defence lawyers, Brian Greenspan, is lending his informal assistance to the family.

Nearly a week after the bodies of the billionaire and his wife were discovered in their North York house, the scene is still being worked on by investigators. Sources have told The Globe and Mail the family is seeking their own answers after previously urging police to conduct a thorough, intensive and objective criminal investigation.

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The Toronto Police Service has confirmed that both Mr. Sherman, 75, the founder of generic pharmaceuticals giant Apotex Inc., and his 70-year-old wife, Honey, a well-known philanthropist, died from "ligature neck compression." Police have deemed the deaths suspicious and have put homicide detectives in charge of the probe even though they have not so far declared it a homicide case.

The service has not publicly released more details, however The Globe and other media outlets have cited police sources saying the early theory was that Mr. Sherman may have killed his wife and then taken his own life. Friends and family have dismissed the suggestion. Through an Apotex spokesperson, the family declined to speak about their intentions on Thursday.

Speaking to The Globe on Wednesday, Toronto Police Chief Mark Saunders declined to comment on the case or the family's criticism of the police until he had met with them.

"Out of respect to the family, which I have a lot of respect for, I want to make sure that the first dialogue that I have is to them and not through the media," Chief Saunders said.

A memorial service for the couple scheduled for Thursday morning at Mississauga's massive International Centre, near Toronto's airport, is expected to draw thousands of mourners, including Prime Minister Justin Trudeau, Ontario Premier Kathleen Wynne and Toronto Mayor John Tory.

Among those assisting the family as it grapples with the couple's shocking deaths is Mr. Greenspan, who has had a long career of controversial cases in the public eye or involving celebrities. Contacted on Wednesday, Mr. Greenspan would say little about the help he is offering, but said he had not been formally retained.

"I knew the Shermans, I knew Barry and Honey. And I am really simply serving as a resource person to the Sherman family," Mr. Greenspan said. "Barry and Honey were people that I knew and very much admired and respected."

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He declined to get into details about what he said would be a "very limited role."

In addition to lawyers, families sometimes hire private investigators in these types of cases, said former Toronto Police homicide detective Dave Perry, now the chief executive of Investigative Solutions Network.

"It's not common but it's not extraordinarily unusual either. A lot of times, especially in death investigations, families have a hard time understanding – and sometimes with good reason – what they're being told by the police," he said.

A private investigator's role would be to conduct a parallel investigation to police, reviewing reports and evidence to determine whether they agree or not with police findings.

Generally, Mr. Perry said, they tend to agree with police findings in death investigations–"not because we want to, but because death investigations are a priority in policing and there are a lot of experienced people tasked to solve the mystery, if you will, and to get the right result."

Nevertheless, he acknowledged those results can be difficult for a family to digest so soon after a tragic loss.

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"Sometimes people have a very, very – understandably – difficult time coming to terms with the fact that a member of their family died in a certain way."

Police continued to examine the Shermans' home on Wednesday, nearly a week after the couple's bodies were found hanging by the mansion's indoor pool.

The Shermans had just become grandparents, their daughter Kaelen was getting married in early May and they were in the process of building a new house.

The house where the Shermans were found dead, in the city's north end, was custom-built in 1991 but had numerous flaws, according to a lawsuit the couple filed against its architects and builders.

It was at that house that the Shermans hosted a fundraiser for the federal Liberals on Aug. 26, 2015, that was attended by 100 to 150 people, with then-party leader Justin Trudeau as the guest of honour – an event that is now under investigation by the federal lobbying commissioner, for potentially contravening the lobbying code of conduct.

About a year ago, on Nov. 30, 2016, Ms. Sherman became the registered owner of a house in Forest Hill that used to belong to the late Al Green, a philanthropist and founder of Greenrock Property Management Ltd.

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"They wanted the house. Mrs. Sherman had approached me, expressing interest and we made an arrangement, it worked out very well … they were going to build a new home," Mr. Green's son Barry said in an interview on Wednesday.

Earlier this fall, the Shermans obtained building permits to demolish Mr. Green's house and construct a new two-storey detached dwelling with an integral garage.

They also listed their North York house for sale.

Demolition at the Forest Hill site began a few weeks ago but has been halted, leaving a barren site surrounded by a plywood-boarded fence in the posh neighbourhood.

With a report from Patrick White