The husband of a woman killed in a Richmond Hill homicide last week says his wife died trying to protect her son who had been struggling for years with mental illness.

In a statement released Monday, Sam Costa said his wife, Karen Costa, and son, Jeffrey Costa "had a strong and undeniable bond."

"This unspeakable tragedy that occurred in our family home last week was the result of a loving and protective mother trying to save her son from harming himself," Costa said in the release.

York Regional Police were called to the Costas' home Thursday, where they found the mother and son deceased.

Police originally described the incident as a murder-suicide to CBC News, but backtracked Saturday afternoon, saying it was too early in the investigation to deem it such, calling it instead a "domestic related homicide."

Jeffrey, 22, struggled with with his illness and the Costa family had been involved with mental health fundraising efforts for the past 20 years, his father said.

"I never thought our lives would be so directly affected and altered by this illness," Costa said, adding that the void created by the sudden loss of his wife and son was "unexplainable."

Costa also thanked police and Western University, where Jeffrey was an undergraduate student.

The university issued a statement Friday saying its community was in mourning over the loss of the "well-known" student.

Karen Costa, 52, was a nurse at the Hospital for Sick Children. On Saturday, the hospital described her as "a dedicated nurse and valued member of the SickKids community."

"As we mourn the loss of Karen and Jeffrey, we do find solace in knowing that they are together in heaven," her husband said Monday.