A 6-week-old boy died late Thursday night after being left in the back seat of his mother's car for an hour as the heat index soared above 100 degrees.

Lisa Marie Morris, 25, of the 2400 block of Patrick Avenue, Hephzibah, was arrested Thursday and is facing a charge of felony murder, said Richmond County sheriff's Sgt. Ken Rogers.

Investigator Thelma Gilchrist said the child, whose name wasn't released, was taken to Medical College of Georgia Hospital in critical condition Thursday afternoon. Sgt. Rogers said the child died at 10:04 p.m.

Investigator Gilchrist said the baby was left in Ms. Morris' vehicle from about 11:30 a.m. to 12:30 p.m. outside Ms. Morris' home. She said the mother apparently forgot the child was inside the car, which had its windows rolled up.

Investigator Gilchrist said police were informed about 2:30 p.m., after Ms. Morris took the infant to MCG.

Ms. Morris told police she had returned home from taking her 4-year-old daughter to the doctor's office and asked her cousin "where's the baby," Investigator Gilchrist said.

After her cousin said she was unaware of the infant's whereabouts, Ms. Morris said she checked the rear seat of her black, 2000 Dodge Neon, Investigator Gilchrist said.

"She told us that the child was unresponsive and was blowing bubbles through his nose and mouth," Investigator Gilchrist said.

The temperature at Augusta's Bush Field Airport at noon Thursday was 95 with a heat index of 104, said Tim Hawks, a National Weather Service meteorologist in West Columbia, S.C. Thursday's high temperature was 101 at 3 p.m., he said.

Police said the child's father and another man were inside the residence, but the father was asleep. Ms. Morris told authorities she and the father had been arguing, which could have caused her to become disoriented.

Chief Deputy Coroner Mark Bowen said an autopsy is scheduled for this morning at the Augusta GBI crime lab.

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