JK didn't intend to just rob the Petits. As a career criminal he had before managed to elude being detected. Now he purposely goes in and makes himself known, brutally beats a sleeping man, goes and wakes up the other members of the house, who were soundly asleep.
No, he was there because he wanted to sexually assault the 11 yr old girl. His excuse was that he just wanted money, but the details of the crime and the way it started do not support that. The robbery was the 2nd reason and what he likely told to Hayes. Hayes wanted money. JK wanted the 11 yr old (and then some money).
Guilty of first degree murder, and everything else.
He deserves nothing less than what he gave his last victims, which was certainly not 'life.'