Allegheny County District Attorney Stephen A. Zappala Jr. alleged Thursday that the 2-year-old girl's cousin intentionally started the March 23 fire in McKeesport.
Zappala said the boy is being evaluated by the Office of Children, Youth and Families, which may start court proceedings to remove him from his family because he has a history of starting fires.
Deputy Fire Chief Don Sabol says the fire started about 11:30 p.m. Sunday at the girls' home and burned houses on either side of the residence.
The prosecutor also says the landlord could be held liable for the blaze if investigators determine that the house had no smoke detectors.
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