DEDHAM, Mass. — A Massachusetts woman charged with killing her 8-year-old son by lighting a hibachi-style charcoal grill inside a bedroom in their apartment and then barricading the door has been found not guilty by reason of insanity.

A Norfolk Superior Court judge on Tuesday acquitted Li Rong Zhang of murder in the January 2011 death of Brandon Yang.

Authorities say the 42-year-old Quincy woman intended to kill herself and her son. They say she blocked the door and lit the grill, filling the room with poisonous fumes. The boy died of carbon monoxide poisoning. His mother, found by another family member, survived.

Multiple medical experts testified that the mother lacked criminal responsibility at the time and exhibited psychotic depression with paranoid delusions and was suicidal.