DENVER -- The man accused of dragging his girlfriend behind his truck will be facing the death penalty if he is convicted.

Douglas County District Attorney Carol Chambers filed paperwork Tuesday to seek the death penalty in the Jose Rubi-Nava murder case.

"A decision to seek the death penalty is among the most significant responsibilities any public official can face. The decision is made only after very careful consideration of the criteria established by the legislature, and the facts of the particular case," said District Attorney Carol Chambers. "This decision will always subject me and this office to greater scrutiny and criticism, not less. Some members of the criminal defense bar are vehemently opposed to the death penalty. They will oppose it under any circumstances even though Colorado law provides for the death penalty when warranted."

Rubi-Nava pleaded not guilty in August. He also argued that he is mentally retarded and can't be tried for first-degree murder.

In a court hearing in August, Rubi-Nava's attorney said he has an IQ of 65. That is lower than the standard generally used to classify someone as retarded. The U.S. Supreme Court has ruled that a defendant must be competent to stand trial and face execution.

Rubi-Nava is accused of killing 49-year-old Luz Maria Francio-Fierros in September 2006.

The case is one of the most gruesome that prosecutors have seen and "a heinous murder" is one of the aggravating factors that a district attorney reviews before deciding on the death penalty.

Rubi-Nava is accused of wrapping an orange nylon strap around his girlfriend's neck and dragging her behind his truck for at least a mile -- while she was alive.

Fierros' mangled body was found early Sept. 18 in a quiet subdivision off Interstate 25, north of Castle Rock, 20 miles south of Denver. An autopsy report said she died from strangulation and massive head wounds.

Investigators have said Rubi-Nava told them he had dragged her behind his car after a violent argument, when he accused her of seeing other men. Both the suspect and the victim were from Mexico and were living together in Glendale, Colo. Authorities have said Rubi-Nava was in the country illegally. Fierros was buried in Mexico.

Chambers said district attorneys review the facts of the murder cases to see if the aggravating factors outweigh the mitigators. The aggravating factors could include but are not limited to; a person already imprisoned for committing a class 1, 2 or 3 felony like murder, a heinous murder, a killing of a witness, laying in wait, and multiple deaths.

Rubi- Nava will next appear in court for a motions hearing on Oct. 22 at 8:30 am in div 1 in Castle Rock.