SCIO, Ore. -- A Scio man arrested for the death of his girlfriend's 2-year-old boy has now been charged with murder, authorities said.

Sheriff's office photo

Mario Juan De Dios Tomas

Saturday morning, the Linn County Sheriff's Office received a call about a dead child at 38106 Gilkey Road in Scio.

Responding deputies and medics from the Scio Fire Department found Samuel Martinez-Castaneda, age 2, not breathing and unresponsive. The child was pronounced dead at the scene.

After a preliminary investigation, deputies arrested Mario Juan De Dios Tomas, 26, for second and third degree assault, first degree criminal mistreatment and unlawful use of a weapon in connection with the child’s death, said Linn County Sheriff Tim Mueller.

On Monday, he was charged with murder by abuse. Officials with the Linn County sheriff's office said the murder count was added Monday to other charges because an autopsy showed the child died of blunt trauma to the abdomen.

De Dios Tomas was also charged with fourth-degree felony domestic assault against the child’s mother. He was lodged in the Linn County Jail.

De Dios Tomas is the boyfriend of the child's mother and has been living at the residence, Mueller said.

The mother's three other children, an infant and two older siblings, were removed from the residence by officials with the state Department of Human Services and released to the custody of their biological father.