Ernestine and Lamar Matthews, both 75-years-old, were found stabbed to death in their Cerritos home in February, 2004. Prosecutors say Cain used a pair of scissors in the attack. They believe the motive was robbery.
The couple was killed as they were preparing to leave on a trip to an Indian casino near San Diego to celebrate their 50th wedding anniversary. Their friends called authorities after they knocked on the front door of the couple's home and got no answer.
Jurors deliberated for two and a half days before recommending death instead of life in prison without the possibility of parole.
Cain will be formally sentenced January 15.
CNS contributed to this story