updated 2/19/2009 8:55:38 PM ET 2009-02-20T01:55:38

A Mexican man accused of killing his girlfriend by dragging her behind a car with a tow strap around her neck pleaded guilty Thursday to first-degree murder.

Jose Luis Rubi-Nava, 38, agreed to plead guilty in the death of Luz Maria Franco Fierros, 49, under a deal with prosecutors who had been seeking the death penalty. They also agreed to drop kidnapping and other charges.

Rubi-Nava now faces life in prison without parole. No sentencing date was set.

Rubi-Nava's attorneys had sought to have him declared mentally retarded, which would have barred his execution under Colorado law, but a judge ruled against them.

Franco Fierros' battered and disfigured body was found in September 2006 near Castle Rock, about 20 miles (30 kilometers) south of Denver. An autopsy found that she died of strangulation and massive head wounds.

Investigators said Rubi-Nava told them Franco-Fierros was alive when he began dragging her.

A Colorado Bureau of Investigation agent testified in 2007 that Rubi-Nava told him that he and Franco Fierros had a violent argument hours before her death, and that Rubi-Nava accused her of seeing other men.

Authorities said both Rubi-Nava and Franco Fierros were Mexican immigrants.

The plea agreement required Rubi-Nava to pay $5,200 in restitution and $91,000 in prosecution costs.

Copyright 2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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