Investigators believe the victim may have initially escaped the building before running back inside to look for family members.
The front of the Hemp Lane house was struck just after 3:15 a.m. on Wednesday, jolting the family from their sleep.
Kegan Thomas, 33, is facing charges of attempted murder, murder, arson, aggravated cruelty to animals, and criminal possession of a weapon.
Before firefighters arrived, a Village of Hempstead fire chief, who is also a Nassau County fire marshal, and another fire marshal who was on his way to work, along with Nassau County police officers, attempted to enter the burning home to rescue the trapped occupant. Officials described the effort as "valiant," but it was unsuccessful.
The fire started in the basement of one home on Briggs Avenue just after 8 a.m. on Thursday and spread to another.
A civilian and firefighter suffered minor injuries after a fire tore through three multi-family homes in Woodhaven, Queens on Tuesday.