Christina Rivers told officers she left her son Mason alone in the living room for a brief period, but the autopsy results told a different story.
While Mason did die as a result of drowning, Sabine Parish's Deputy Coroner Ron Rivers says the child also tested positive for methamphetamine in his system and Christina Rivers did, too.
The deputy coroner says a witness saw the child unattended around 10:30 that morning. Sometime between then and the 911 call at 2 p.m., Deputy Coroner Rivers believes, the child got into the water and was there for at least an hour.
Christina Rivers reportedly declined to give detectives an interview concerning Mason's death.
The deputy coroner says he and Christina are second cousins.
Rivers turned herself into the Sabine Parish Detention Center on Monday, August 7.