SAN DIEGO (AP) — A man pleaded not guilty Monday to killing his stepmother and half-brother to keep them from talking about his alleged sex abuse of another family member, authorities said.

Marco Antonio Valadez, 47, entered pleas to two counts of murder with special circumstances that, if convicted, make him eligible for the death penalty or life in prison without chance of parole, the San Diego County district attorney’s office said in a statement.

Valadez is accused of shooting Raquel Pitsenberger, 55, and 36-year-old Marco Valadez Jr., both of San Diego, at a relative’s Imperial Beach home on Dec. 4. He also is charged with sexually abusing an 18-year-old family member two days before the killings, prosecutors said.

The DA’s office didn’t release details of the alleged attacks.

The shootings stemmed from a confrontation “in which he was trying to silence family members who were potential witnesses following the disclosure of his sex crimes,” the DA’s office statement said.

Valadez was captured in Mexico and returned to the United States on Dec. 16, authorities said.

The murder charges carry the special circumstances of killing a witness, multiple homicides, firing a gun resulting in death and committing a crime while on bail, authorities said.

The sex abuse charges carry an allegation that Valadez is a habitual sex offender. He was convicted of forcible rape in 1998 and has several other felony convictions, prosecutors said.