In the criminal complaint, Ada County prosecutors say 27-year-old Monique Osuna murdered Emrik, repeatedly striking and kicking him - possibly hitting him with items like frying pans, wooden spoons, or a back scratcher
The document also says she may have made him do constant physical exercises like jumping jacks and wall sits - all while withholding food from him and locking him in a small closet to sleep at night.
Prosecutors accuse the boy's father, 29-year-old Erik Osuna, of allowing his son to be in her custody, knowing she was doing this, saying he chose not to seek medical attention for the injuries.
They also claim he hid surveillance video to prevent it from being used in the investigation.
The Ada County Prosecutor's Office provided a statement Wednesday: "We send our condolences to the extended family, however we cannot comment on pending litigation."
Boy who was sent to Idaho to live with dad because of abusive mom dies at age 9
People across Idaho have been advocating for justice, like at a vigil shortly after his death where people wore blue - a color associated with child abuse prevention.
Santa Ana police worked with Meridian police to transport the boy's body back to Southern California for proper burial organized by his aunt and uncle who once cared for him.
Santa Ana police investigated an earlier case involving the boy's biological mother, Sacil Lucero, who was arrested on child abuse charges three years ago. Emrik's younger siblings from another father were harmed in that case. He lived with his aunt and uncle for a time before he moved to Idaho to be with his father.
Lucero had a pre-trial hearing on that case last week.
Investigators from Idaho were in Southern California Wednesday for Emrik's funeral and had plans to discuss both cases with Santa Ana PD to see if there are any connections.