York Regional Police say a fire back in May that killed two children is now considered suspicious.
The fire broke out on a Sunday morning at a home on Bur Oak Avenue in Markham.
A 12-year-old boy was found dead in the basement two days later.
Police say his six-year-old brother died in hospital in July.
Their mother and another brother survived and police say the father wasn't home at the time.
Police are now searching for whoever is responsible. "Somebody out there knows something about this, either the family or the fire and why the fire was set, and we're looking for those people to come forward," says Sgt. Andy Pattenden.
He says police have spoken with the surviving family members but have no clear suspects at this time.
Anyone with information is asked to contact the York Regional Police Homicide Unit at 1-866-876-5423 ext. 7865 or Crime Stoppers at 1-800-222-TIPS.