Police say the teen, identified as George Almaraz, was abused, tortured and then killed allegedly by his stepmother, 35-year-old Jessica Paola Grajeda.
The boy's father, 32-year-old George Luis Almaraz, was also arrested. Police say he was aware of the abuse but did nothing to stop it or seek medical attention for his son.
The family lived inside a lower-level corner apartment unit at the end of Del Rosa Avenue in Pomona.
Exactly what happened inside is unclear. Details about the boy's cause of death were not immediately disclosed, but police said there was a history of abuse at the home going back at least four months.
Neighbors at the apartment complex, who saw the boy being removed from the home by paramedics on Tuesday, were stunned at the allegations about what led to his death.
"She's a monster. She's not a stepmother. You don't treat kids like this. He's 16 years old. He had a future ahead of him," said neighbor Phillip Sayegh. "That life was taken, and justice needs to be served and delivered to that kid."
MORE | Father, stepmother arrested in murder, abuse of 16-year-old boy in Pomona
Sayegh said he witnessed emergency officials arrive on scene, then saw the teen being carried out in a stretcher.
"From the way he looked, it looked like he was done," Sayegh said.
Fellow neighbor Javier Romero said he witnessed paramedics trying to save the boy's life.
"The ambulance came right away, really fast, and they take the little boy...and just doing CPR, and then that's it," Romero described.
The teen was transported to a local hospital, where he was pronounced dead.
There were five other children in that household at the time, ranging from 1 to 13 years old. The other children have been taken into protective custody and turned over to the county Department of Children and Family Services.
Investigators at this point do not see any indication that the other children were abused.
The Los Angeles County District Attorney's Office has filed charges of murder, torture, and child abuse resulting in death, as well as three counts of child abuse against Grajeda.
The victim's father is facing one count of felony child abuse under circumstances likely to cause great bodily injury or death.
A preliminary court hearing was held Thursday. Bail for Grajeda was set at $2 million and her arraignment was set for June 8.
Almaraz was released on his own recognizance with electronic monitoring. His arraignment is also June 8.
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