Fire officials are still investigating the cause of an apartment building fire on Tuesday that killed a 4-year-old boy (a 5-year-old, according to some reports). The fire broke out at about 1:30 p.m. at the West Park Apartments, a 19-story public-housing building on Busti and Holden streets.

The child’s mother and 3-year-old brother were injured in the fire. The mother and a male resident of the building saved the younger child from the apartment engulfed with fire. Then the woman returned to the apartment and tried to rescue her older son but was badly hurt, Philly.com reports. The firefighters found the boy alive under a bed, but he later died in the hospital.

Fire officials said a burst main near 42nd and Market streets that required the evacuation of a fire station across the street from high-rise slowed response time.