Surjit Dosanjh has been in custody since the blaze early Monday, when 66-year-old Elaine Leznoff was killed.
Police say 13-year-old Kalvin Dosanjh-Leznoff remains in hospital and is not expected to survive.
Sgt. Stephanie Ashton from the region's homicide investigation team says Dosanjh has been estranged from his family since earlier this month and was not living in the home at the time of the fire.
Ashton says the Leznoff family is grateful for the support they've received but would like to grieve in private.
Thirty-seven-year-old Dosanjh was expected to appear in court Friday.
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