Five years ago, Canadian billionaires Barry and Honey Sherman were found strangled to death in their home.
Since then, despite a hefty $10 million reward, their murders remain unsolved.
And now, in an effort to restart the investigation into his parents' killings, son Jonathon Sherman has added an additional $25 million as a reward for information that could help arrest and convict the culprit.
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Marking the five-year anniversary of the killings, Jonathon said in a statement to Canada's CBC News: "Every day since then has been a nightmare. I have been overwhelmed with pain, loss, and sorrow and these feelings only continuously compound.
"This immeasurable pain is felt every day when I realise that my own two children will never have the privilege of meeting my parents who made their lives possible for me and my husband."
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He continued: "Closure will not be possible until those responsible for this evil act are brought to justice.
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"I hope for the day when I make this payment, as it will finally allow for healing."
Barry Sherman, 75, had been the founder and chairman of drug company Apotex, and was one of the wealthiest men in Canada.
At the time of their death, Barry and Honey's net-worth was estimated to be around $3 billion, according to Forbes.
At first, police suspected that the philanthropic couple might have died by suicide - a theory Jonathon had shut down.
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However, there were no signs of forced entry into their Toronto mansion.
Six weeks after the bodies were discovered, Toronto police confirmed that evidence found they were victims of a homicide and had been targeted.
Last December, police released footage of a person walking near the Shermans' home on 13 December, 2017 - the day that autopsies suggest the couple were killed.
Although police were unable to identify the person in the video, they have been identified as a suspect.
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Authorities noted that the suspect appeared to be between 5'6" and 5'9", and appeared to have an unusual strut that saw their right heel kick up while walking - though their gender, race, age, or weight couldn't be determined.
Unfortunately, since the footage was released, no one has come forward.
In the past, the late couple's four adult children have criticised Toronto Police and hired their own private investigator to look into their parents' deaths.
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In his latest statement, Jonathon said that he looks forward to the day he can pay the promised $35 million to someone, 'as it will finally allow for healing'.
Ali Condon