just seen the clear photo of junes body for the first time.i must say she looks a terrorable mess.how one could do that to a person who bought you up with love and gave you all the best things in life .after your real parents had disowned you is incomprehensible.and all for what bits of paper.greed brings out the worst in everybody 
Greed was likely the deciding factor and motive but he had issues with his parents. He felt they were controlling his life among other things. That made it easier to kill them. Killing someone you love for money alone is hard to do.
I was brought up with a strong sense of morality and only believe in killing in self-defense/defense of others. On the opposite end there are people totally lacking in respect for life who will kill for a simple insult, to rob $5, for the sport of it just to see what it is like, to join a gang... Most American murders are committed in inner cities by people who have no respect for life at all. Jeremy might not have been as callous as these thugs but killing is horrible period.
I recently learned of a case where a woman poisoned her husbands and when police were getting close she poisoned her daughter and wrote a fake suicide letter for her so her daughter could be blamed for the murders. Luckily she didn't die and computer analysis proved the letter was typed up while the daughter was in school. How could you do that to your own daughter? Some people care only about themselves and will do anything for their own benefit.
Murder by Muslim extremists is particularly pointless. Their end is simply to kill innocents for sport essentially until they can be stopped. That is more scary than people who kill for monetary gain.