The first Bexar County Sheriff's Deputies arriving at a South Bexar County home found a naked, badly wounded woman on a door step.
Carol Sanchez, 35, had been stabbed repeatedly. She was at the home of the neighbor of her boyfriend Rogelio Nava.
"She was hysterical – very hard to calm down," said Deputy Mary Saenz.
Saenz said that before Sanchez was taken to the hospital, she told her what had happened.
"She said they were inside the house and they were about to have sex when her ex-husband hit her partner on the back of the head and that he was in the house stabbing him," Saenz said.
Nava was killed. Sanchez survived.
Castillo, prosecutors say, had broken into Nava's home and was waiting for the couple to come home in the early morning hours of Aug. 15, 2010.
He is on trial for capital murder but is not facing the death penalty.
If he is found guilty Castillo, will be sentenced to life in prison without the possibility of parole.