Whether or not the suspect in a brutal murder case is mentally retarded is being debated this week in a Douglas County courtroom.

Jose Rubi-Nava is accused of dragging his girlfriend to death.

If Rubi-Nava is found to be mentally retarded, he cannot face execution if he is convicted. He has pleaded not guilty.

Prosecutors said 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 has an IQ of 65.

In opening statements Monday, the prosecution argued that Rubi-Nava was clever and said he was smart enough to live a normal life in Colorado. He was teaching people to play chess and dominoes and was learning to speak English. He tried to get into the United States six times and got in the seventh time. Rubi-Nava was working two jobs -- one as a landscape company and another at McDonald's -- and sending back $300 per month to family in Mexico.

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.

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 car, tried to escape and made arrangements to pick up last check so he could go back to Mexico.

When interviewing family in Mexico, nobody referred to him as being retarded, prosecutors said.

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.

His family is expected to testify later this week. The mental competency hearing is expected to last for days.

Judge Paul King will determine whether or not Mr. Rubi-Nava is mentally retarded or take the matter into advisement.

To note, in order for an individual to be found legally retarded three factors must be met: the individual must have an IQ below 70, the mental retardation must manifest itself before the defendant has reached the age of 18, and there must be significant deficiencies that impact major life functions.