As reported by the Arizona Star, police say Roman Barreras's mother, Raquel Barreras, 39, allegedly starved the boy, made him live behind the house in a tiny room, and after his death, disposed of his remains in that room, in a toy chest that she didn't bother to take when the family moved.
The discovery has shocked relatives, neighbors and the police.
"For a young child, one of the most innocents in our community, how anyone can do that to someone is very difficult for anyone to understand," Tucson Police Chief Roberto Villaseñor told reporters at a press conference Wednesday, a day after the discovery.
Raquel Barreras has been charged with murder. Both she and the boy's father, Martin Barreras, 45, are also charged with child abuse.
Villaseñor said police officers had been to the house before, mostly responding to truancy complaints about the family's other children: a 12-year-old son and three daughters ages 19, 7 and 4. He said that, during those visits, there were no outward signs of the children being abused.
At a press conference held by a local group, Homicide Survivors, relatives expressed their grief.
"The Barrerases are in shock," added Martin Barreras's cousin, Oscar Romero. "To find out one of their own has been taken from us, especially a child, is the worst nightmare. I don't know what caused this. Some of us are asking the question, and we want to know and find out the truth."
The relatives, who say the parents were very secretive and moved often, added that they called protective services for help.
A spokeswoman for the state's Division of Child Safety and Family Services confirmed to the Star that caseworkers had contact with the Barreras family, with the last involvement in August 2012. More information was not immediately available, said agency spokeswoman Jennifer Bowser.