CASTLE ROCK, Colo. -- A hearing resumed Tuesday to determine whether a man accused of dragging his girlfriend to death behind a car is mentally retarded.

Jose Luis Rubi-Nava 37, is charged with murder and kidnapping in the September 2006 death of Luz Maria Franco Fierros. Her mangled body was found early Sept. 18, 2006, 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 were from Mexico and were living together in Glendale, Colo. Authorities said Rubi-Nava was in the country illegally.

At a hearing in January, a state mental health doctor testified that Rubi-Nava is not mentally retarded, and said he has decent communication skills, follows instructions and can do simple math problems.

But a defense psychologist has said Rubi-Nava is retarded.

If Rubi-Nava is declared mentally retarded, it would prevent prosecutors from seeking the death penalty.