Peel police have arrested a woman and her common-law husband in connection with the death of a Mississauga man and his mother, who police say were killed three years apart under mysterious circumstances and in the same home.

Melissa Merritt, 33, and her common-law husband Christopher Fattore, 36, were arrested in Nova Scotia on Tuesday morning and charged with two counts of first-degree murder after police determined that both Caleb Harrison and his mother, 63-year-old Bridget Harrison, were asphyxiated in their Mississauga home.

Caleb, 41, was found dead in his family home on Pitch Pine Crescent last August. His death was deemed suspicious by police and an autopsy later ruled the death a homicide.

His mother Bridget’s body had previously been discovered at the bottom of a staircase in April 2010. Police also considered her death to be suspicious but the case remained unsolved for years.

Peel Regional Police Insp. George Koekkoek told reporters on Tuesday that an investigation into Harrison’s death revealed that both mother and son were killed by asphyxiation.

Police also say they are now reopening an investigation into the death of Harrison’s father, 65-year-old Bill Harrison, who also died unexpectedly in the same Mississauga residence in 2009.

His death was originally thought to have been caused by natural causes but has since been reclassified in light of the recent investigation.

“That said, we have no information at this time to declare that it was a homicide,” Koekkoek said. “His death remains under investigation.”

Neighbours in the area say they were suspicious of the string of sudden deaths at the Harrison home.

“The dad died, the mom died and now the son? It’s pretty weird,” said one neighbour.

Donna MacCormack, a resident in the area, told CTV Toronto that she remembers Caleb Harrison as a kind and loving father.

“Large personality, large smile, large bear hugs, his kids were great,” she said. “There’s not a day that goes by that I don't look at the house and my eyes fill up with tears."

Merritt and Harrison married in 2003 and had two children before filing for divorce.

Police say Merritt had been charged with parental abduction of the couple’s children in 2009, on the same day Bill Harrison died.

Merritt comes from a police family -- her father is a retired Toronto police officer and her brother currently works on the force.

Police say Merritt met Fattore, her current common-law husband, in 2005 and the couple moved to Bridgewater, N.S., shortly after Harrison’s death.

Police would not reveal if any other suspects are being investigated in relation to the case.

Officials say they have been in contact with the Harrison family and have notified them of the arrests.

Merritt and Fattore are expected to appear in a Halifax court on Wednesday and will be sent back to Ontario on Friday to face charges at a Brampton court.

With a report by CTV Toronto’s Tamara Cherry.