An 11-year-old boy found dead at his family’s Los Angeles home in August had been confined to a wardrobe by his mother for three years, it has emerged.

When Yonatan Daniel Aguilar vanished in 2013, his mother, Veronica Aguilar, told people he had been sent to live at an institution in Mexico. Despite previous allegations of abuse, the police, social workers and school officials never investigated. Even the boy’s stepfather, Jose Pinzon, appears to have been unaware that Yonatan was at home the whole time.

According to court records obtained this week by the Los Angeles Times, Aguilar, 39, kept her son locked in a bedroom cupboard, where he was sedated with a sleep-inducing syrup. Police found the child’s malnourished body spotted with pressure sores from the tiled floor and surrounded by cups of the liquid medication.

Pinzon told police he only learned his stepson had died when his wife told him on 22 August and asked him to care for her three remaining children. Pinzon assumed she would travel to Mexico to bury Yonatan’s body, but instead she led him to the wardrobe, where he found the boy’s lifeless body, weighing little more than 15kg, in a space too small to stretch his legs.

Pinzon then ran to a nearby convenience store in the Echo Park neighbourhood, where he called the police. Aguilar has pleaded not guilty to murder.