Police went to 84-year-old Joyce Dexter's Salt Lake City home on Oct. 3 after neighbors heard screams and called 911. Officers found Zachary Cole Weston standing over Dexter's body while holding a bloody knife, according to court records released Friday.
Weston had blood on his clothing and hands and later told investigators he had also cut his grandmother's jugular, the records said.
The 21-year-old has been charged with aggravated murder, a capital offense. Family members told The Salt Lake Tribune that Weston suffers from mental illness.
He was arrested in 2010 after he was accused of pushing his mother and striking a police officer. He pleaded guilty to one of two assault charges.
As part of his sentence, he was ordered to undergo a mental health evaluation and complete any recommended treatment, but he was charged Aug. 9 with two counts of assault and interfering with a police officer during an arrest for slapping one hospital employee and punching another in the face, the Deseret News (http://bit.ly/RWtj2D ) reported.
He was also charged with assault for hitting his father during a Sept. 27 argument.
Salt Lake County District Attorney Sim Gill declined to comment Friday on a possible motive in the stabbing, but he praised police for responding so quickly.