DENVER -- A Douglas County judge ruled Friday that the suspect in a brutal murder case is not mentally retarded and prosecutors can proceed with their death penalty case.

Prosecutors said Jose Rubi-Nava scored an 81 on an IQ test; anything under 70 is considered mentally retarded. Rubi-Nava's attorney had argued that in a different test, it showed he had an IQ of 65.

The district attorney could not discuss the ruling because of a protective order, but a spokeswoman said the DA will move forward with the death penalty case.

Rubi-Nava is accused of killing his girlfriend, 49-year-old Luz Maria Francio-Fierros, in September 2006. Even though he had a girlfriend whom he lived with, he was also seeing another girl in the United States, prosecutors said.

Prosecutors said Rub-Nava killed his girlfriend after a passionate argument about another man. He 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.

He has pleaded not guilty.

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.

Douglas County prosecutors argued that Rubi-Nava is a predator, not mentally retarded. They said he tried to cover up his crime, tried to hide his car, tried to escape and made arrangements to pick up his last check so he could go back to Mexico.

Prosecutors said that when they interviewed his family in Mexico, no one referred to him as being disabled.

His family didn't drink and had no history of abuse, but his father was murdered when he was young. After that, Rubi-Nava had to go to work to support his family and he only had five to six years of education.

But even then, he was very good at math and could calculate numbers in his head faster than others could use a calculator, prosecutors said. After the crime, he told all his friends and relatives to tell everyone he was crazy, prosecutors said.