Dwayne Biddersingh died in 1992. He fell 22-storeys from an apartment building in Toronto's Parkdale neighbourhood.
"It was a difficult decision. The boy's remains have been here for a long time but we want to be thorough, we want to make sure there was no foul play involved in his death," said Det.-Sgt. Steve Ryan.
His death was deemed a suicide.
Dwayne's biological mother, Opal Austin who lives in Jamaica, reached out to police here and shared her suspicions.
"She's curious whether foul play was involved and so this is going to help in determining that. But there's nothing to suggest it was nothing more than a fall," said Ryan.
Police decided to look again at the circumstances surrounding the boy's death after the remains of his sister were identified in Nov. 2011.
Melanie, who was 17 when she disappeared, was never reported missing. Her remains were found inside a suitcase that had been set on fire.
The children's father Everton Biddersingh and their stepmother Elaine Biddersingh face first-degree murder charges in Melanie's death.
Dwayne's remains will go to the coroner's office for a second autopsy.