Denton man described as "serial predator" by prosecutors to face 50 years in prison without parole

A Denton man who was described by Collin County prosecutors as a "serial predator" is set to spend the next 50 years in prison after he was convicted of sexually abusing a girl who lives with autism.

District Attorney Greg Willis announced the sentence for 52-year-old Marty Duwayne Griego on Tuesday. Griego was found guilty of continuous sexual abuse of a disabled individual, which carries no eligibility for parole.

Willis said Griego had an ongoing relationship with the child's family, which gave him access to the victim. The abuse, Willis said, lasted for a year, ending when the girl turned 15 years old. Willis said the crimes only came to light when Griego assaulted the girl in front of another child, who immediately made an outcry to authorities. That was when the Plano Police Department was notified.

According to Willis, the girl underwent a medical exam that turned up DNA evidence linking Griego to the abuse. A forensic interview interview followed at the Children's Advocacy Center of Collin County, where Willis said she shared detailed accounts of repeated abuse in Plano, Carrollton and Corpus Christi.

While Griego was convicted in April of 2026, Willis said jurors also heard evidence that Griego had sexually abused another child along with sexually assaulting an adult. The adult, Willis said, reported the crime after Griego was arrested.

"A serial predator who preyed on a severely disabled child will never walk free again," Willis said in a statement. "This 50-year, no-parole sentence delivers the justice our most vulnerable victims deserve." 

If Willis is still alive at the end of his prison term, he will be 102 years old upon release.