And of inexperience.
I think he'd thought for a long time about what he wanted to do, possibly even studied other attackers, but if it's true that he wanted to rape them but then killed them in a panic, it shows that it didn't pan out the way he'd planned. The reality of what he needed to do to control others with independent thought and will was different to his expectations.
Yes, the girls were abducted, yes, they were killed, but if he killed them in a panic to try and regain control rather than that killing in that way being the goal, that shows that the offender wasn't experienced and had no idea what to do except act out with extreme violence.
MOO