Eric Lawson, 23, was charged Sunday with three counts of murder and nine other charges, including arson, for the deaths of Breiana Ray, 22, her mother, Gwendolyn Ray, 50, and his 10-month-old son Aiden Lawson, the St. Louis Post-Dispatch reported.
Lawson allegedly told police he was upset with Breiana Ray over unspecified reasons, so on Saturday night he went to the St. Louis apartment she shared with her mother and children, armed with a semiautomatic gun. Once there, Lawson said he shot Ray and her mother.
He also told police he started two fires before leaving.
When police arrived, they found the women dead, as well as the infant, who died of smoke inhalation.
Another child of Breiana Ray's, a 3-year-old girl whose name has not been released, was taken to a hospital where she was listed in critical condition, the newspaper said.