BRAMPTON

A 33-year-old woman and her partner face murder charges for allegedly killing her ex-husband and former mother-in-law in Mississauga.

Arrested in Nova Scotia, Melissa Merritt, 33, and her common-law husband Christopher Fattore, 36, will be returned to Ontario this week on charges of first-degree murder.

Peel Regional Police alleged the asphyxiation of Caleb “Cal” Harrison, 41, at his Pitch Pine Cres. home last summer enabled them to make sense of a puzzling case.

“It was apparent early on that his death was a case of homicide,” Insp. George Koekoek said Tuesday.

He said evidence gathered during the probe into Caleb’s murder “opened new avenues of investigation” into the “suspicious” death of his mother, Bridget Harrison.

“This new information led officers to the determination that her death was also a homicide,” Koekoek explained.

Police also took a fresh look at the “sudden passing” of Caleb’s father, William “Bill” Harrison, who was found dead in a bathroom at the house on April 16, 2009.

However, investigators have no evidence the father’s death was a homicide.

Caleb was last seen alive on Aug. 22 coaching his kids’ baseball game in Eringate Park. His children — then 10 and 12 — went home after the game with their mom and Caleb headed to his parents’ house.

The divorced dad was found dead the next day in the Burnhamthorpe Rd.-Winston Churchill Blvd. area house, which he moved into — along with his two kids — in 2009, after serving time in prison for impaired driving causing death.

Caleb’s mother, Bridget, was found dead at the bottom of a flight of stairs in the family’s home on April 21, 2010.

Police initially had “no conclusive evidence” the retired Peel and Toronto District School Board teacher was murdered, Koekoek said.

So the case remained open and unsolved for over three years.

Investigators have since determined both mother and son died of asphyxiation.

Merritt and Fattore were in the news in 2012 when the Stratford-area house they were renting burned down, but the fire was not connected to the murders, according to police.

Merritt was also arrested for parental abduction in 2009 and later convicted.

Koekoek said Caleb divorced Merritt in 2005 and she began a relationship with Fattore that same year.

The kids have lived with their mom and her new partner since their dad’s slaying, Koekoek said. And about four months ago, the couple relocated to Bridgewater, Nova Scotia, with Merritt’s kids and the children they have together.

Peel police arrested Merritt and Fattore Tuesday with help from the RCMP and Halifax Regional Police.

The couple will likely appear in Brampton court Saturday.