The Sherman family's decision to hire private investigators to separately probe the deaths of their mother and father could cost up to $1 million.

And while similar investigations may not be as costly, they can still run into the tens of thousands of dollars, making that option cost prohibitive for many Canadians.

"The first thing I tell [the family] is that they can get quite expensive," said David Perry, a Toronto-based private investigator. "It's a very big strain on people that don't have the financial resources to do it."

CBC News has learned that the Shermans have hired some of the most seasoned investigators to look into the case. With Toronto lawyer Brian Greenspan at the helm, the investigative team is led by former homicide detective Tom Klatt. The team includes former Toronto homicide detectives Mike Davis and Ray Zarb and former detective Martin Woodhouse. It also includes former Toronto police forensic specialists Dennis Buligan and Al Benton.

As well, the Shermans have hired David Chiasson, the former chief forensic pathologist for Ontario, who conducted a second autopsy on Barry and Honey Sherman, the billionaire Toronto couple found dead at their home in December. Barry Sherman was the founder of generic drug giant Apotex.

"I wouldn't be surprised at the end of the day if their cost of that investigation is going to be in the $500,000 to million-dollar range," said Brian King, a Toronto-based private investigator whose cases have included aiding in overturning the wrongful murder convictions of Robert Baltovich and Steven Truscott.

Multiple killers

CBC News has also learned that private investigators believe that Barry and Honey Sherman were murdered by multiple killers.

While investigators will work pro bono on select cases, a typical investigation can be anywhere between $30,000 to $100,000, depending on time spent and complexity of the case. (Investigators normally charge by the hour.)

They can last anywhere from few weeks to do a quick review of the case, or from six to eight to 12 months.

For some clients of private investigators, the expense is money well spent.

Joanne MacIsaac hired Perry as part of her investigation into the death of her brother Michael, who was shot by police on Dec. 2, 2013, as he ran down the street naked. She said it has cost her upwards of $60,000.

The Special Investigations Unit cleared the officer involved, a conclusion the family disputes.

"We quickly knew we needed to have everything documented and our own independent facts to be able to go against them."

'It's worth it'

As part of their private investigation, MacIsaac has hired two forensic scientists to review the 911 call, a ballistic specialist from the U.S. and a trauma specialist. She also paid for a second autopsy and 3D forensic scan of the scene of the shooting.

"It's worth it," she said of the costs.

But Perry, who wouldn't discuss the MacIsaac case, said he always advises his clients that it's quite possible, following their own investigation, they will reach the same conclusions as the police.

"They need to know going in that the likelihood of us disagreeing with the police is far less than the likelihood of us agreeing with the police because [they] tend to do a very good job of policing death investigations."

Still, both King and Perry say they can offer an independent look from a team of professionals to ensure everything that was supposed to be done, was done, and the police conclusions were appropriate.

This is so high profile, they're going to be very cautious about sharing any information that may tend to taint their investigation any way down the line - Brian King, private investigator

As for police co-operation, that can vary. In the Sherman case, as the family investigators work in parallel, but separate from, the police, it's unlikely detectives will share any information they obtain, King and Perry said.

"This is so high profile, they're going to be very cautious about sharing any information that may tend to taint their investigation any way down the line," King said.

"There are protocols that the police have to follow just by virtue of the fact that they potentially could be testifying in a criminal case later and or a coroner's inquest."

No access to crime scene until police finished

That means it's highly unlikely that the family's private investigators will get any access to the crime scene — the home of the Shermans — until police are finished.

By the time the private investigators get inside the house, the scene will have been contaminated by all the forensic work done in advance, Perry said.

While that doesn't mean they won't uncover some new piece of evidence, "I don't think they could send a team of forensic investigators in there after the Toronto police leave and expect they would find anything that the Toronto police didn't already find," he said.

While this may limit the scope of their own investigation, a private team can hire their own pathologist, as the Sherman family has done, and re-interview neighbours or any potential witnesses.

King said police sometimes try to hamper a private investigator's efforts.

When he was hired by the family of Raymond Lawrence, a young black immigrant and alleged drug dealer who was shot by police in 1992, the police advised witnesses they were under no obligation to talk to private investigators.

"More or less inferring and implying they they shouldn't co-operate. So sometimes police can have a negative effect on parallel investigations."

Police can be co-operative

Perry said he mostly gets involved after police have concluded their own work, and at that point, detectives can be very co-operative. He said he has been given access to autopsy and crime scene photographs, witness interviews, police officer notes, forensic and post mortem reports — all of the things that would help an investigator come to a conclusion of how it is that this person died.

"I've had police services sit down with me, with investigators and sometimes with the senior officer who will say 'you know, we'd appreciate it if you would share with us anything that you find that is different than what we have."