Police Thursday night were investigating the suspicious death of a 6-year-old boy in Southwest Philadelphia.

Medics and police responded about 7:20 p.m. to the child's home in the 2100 block of South Daggett Street and medics pronounced the boy dead at 7:29 p.m., said Lt. John Walker of Southwest Detectives.

The boy, who was hearing-impaired and had a twin brother, had been playing outside with a water gun when around 4:45 p.m. he stepped inside and slipped on the kitchen floor and injured his head, according to his 39-year-old stepfather, Walker said. The boy's mother was at work at the time.

The stepfather placed the boy in bed upstairs and then went outside to smoke a cigarette, Walker said. About 15 minutes later the stepfather found the boy gasping for air and moved him to another bedroom before returning downstairs.

Around 5:40 p.m., the stepfather found the boy unresponsive, Walker said. The stepfather did not say why he waited an hour and forty minutes before calling for emergency help.

Police were awaiting the results of an autopsy to be performed by the Medical Examiner's Office.