Daniel Corby, who turned 4 last Monday, was pronounced dead by medics near a San Diego police substation on El Camino Real in Carmel Valley about 10 a.m. Saturday, according to the county Medical Examiner's Office.Minutes earlier, the boy's mother, 36-year-old Patricia Corby, had flagged down a patrol sergeant driving out of a parking lot at the precinct house and asked for help with her son, who was unconscious and not breathing in her car, SDPD Lt. Ernie Herbert said.After questioning Corby, detectives arrested her on suspicion of murdering the child.San Diego police sources told 10News Corby was a stay-at-home mother pushed to the edge handling a difficult child with autism. They say Daniel was drowned and his mother unsuccessfully tried to drown herself before driving her son to a nearby police station. Investigators with the police department's Homicide Unit would not confirm that information. Corby was described as being in a state of shock as she watched officers trying to revive her son. An autopsy has been conducted, but a cause-of-death ruling was on hold pending completion of further postmortem tests, the medical examiner reported.Police disclosed no suspected motive for the alleged domestic slaying in the 4600 block of Torrey Circle. The boy's father was at work at the time of his son's death, Herbert said.Neighbors told 10News he is devastated and has moved from the apartment. A family member who refers to herself as "Cousin Wendy" posted a comment on 10News.com about the tragedy, saying in part, "Daniel was a very loved little boy he will be missed by many. We can only wish that this had never happened." Corby was booked into Las Colinas women's jail and was being held without bail pending arraignment, scheduled for Wednesday afternoon.