A common-law couple has been arrested in Nova Scotia and charged in the deaths of a mother and son from Mississauga, Ont., who police say were killed three years apart.

Earlier today, Peel Regional Police said they had made arrests in the death of Caleb Harrison, 41, who was found dead in his Mississauga home on Pitch Pine Crescent last summer.

Harrison was discovered dead inside his home on Aug. 23, 2013. A co-worker found him there after he had failed to show up to work.

His mother, Bridget, had died in the same home in 2010, at the age of 63. An obituary that was published after her death said only that she had "passed suddenly."

Her death had been considered suspicious, but police had not initially deemed it a homicide. However, after Caleb Harrison was found dead, police say they undertook "new avenues of investigation" and determined that his mother had been killed as well.

At an afternoon press conference Tuesday, police said that both mother and son died of asphyxiation.

William Harrison, the husband of Bridget and father of Caleb, died in 2009 at the age of 65.

Police said they initially believed he had died of natural causes, though the cause is now considered unknown and is currently under investigation.

Arrests made in Bridgewater

Melissa Merritt, 33, and her common-law husband, Christopher Fattore, 36, were arrested near Bridgewater, N.S., on Tuesday. They are jointly charged with two counts of first-degree murder.

Police say Merritt is the ex-wife of Caleb Harrison.

Insp. George Koekkoek said Tuesday that Merritt and Harrison had two children together.

The couple split in 2005, which was the same year Merritt met Fattore.

Koekkoek said that Merritt had previously been convicted of parental abduction of the children she had with her former husband.

He said that the abduction occurred around the same time that Harrison’s father died.

Police believe that Merritt and Fattore had been living in Nova Scotia for about four months prior to their arrest.

They will be transported back to Ontario and are due to appear in a Brampton court on Friday.

With files from the CBC's Ivy Cuervo and The Canadian Press