Canadian police said they were investigating the mysterious deaths of Barry Sherman, founder of Canadian pharmaceutical firm Apotex Inc, and his wife, Honey, one of the nation's wealthiest couples whose bodies were found in their mansion on Friday.
Police said they learned of the deaths after responding to a midday (1700 GMT) medical call at the Sherman's home in an affluent section of northeast Toronto.
Two bodies covered in blankets were removed from the home and loaded into an unmarked van on Friday evening.
A real estate agent discovered the bodies in the basement while preparing for an open house, the Toronto Globeand Mail reported, citing a relative.
The Shermans recently listed their home for sale for nearly $5.4 million.
"The circumstances of their death appear suspicious and we are treating it that way," said Constable David Hopkinson.
Homicide detectives later told reporters gathered outside the home that there were no signs of forced entry.
Their neighbours, business associates and some of Canada's most powerful politicians said they were saddened by the deaths.
Prime Minister Justin Trudeau tweeted out a special condolence message:
Toronto Mayor John Tory also tweeted that he was "shocked and heartbroken."
In a separate statement, Tory said, "Toronto Police are investigating, and I hope that investigation will be able to provide answers for all of us who are mourning this tremendous loss."
Condolences poured in from Canada's business community and political circles.
One of the wealthiest Canadian couples
Sherman, 75, founded privately held Apotex in 1974, growing it by introducing large numbers of low-cost generic drugs that took market share from branded pharmaceuticals.
He stepped down as chief executive in 2012 but remained executive chairman.
Forbes has estimated Sherman's fortune at $3.2 billion.
Apotex is the world's No. 7 generic drugmaker with 11,000 employees and annual sales of more than 1.5 billion in more than 45 countries, according to its website.
The couple was known for their philanthropy, giving tens of millions of dollars to hospitals, universities and Jewish organisations, Canada's CBC reported.
"They were extremely successful in business, but also very, very giving people," former Ontario Premier Bob Rae told CBC.
"It's going to be a very, very big loss."