This could simply mean he has controlled his "urges" up until now, or that he has not been caught...
I agree with you clu.
Also, a sex crime may not have been the motive for her murder. It might just be something he did either prior to or after the murder.
We all know that sexual assault (rape included) isn't a crime that involves sexual desire. It is a crime of violence, agression and power. It is used to degrade the victim. It is usually about power, control, rage, and some of them get satisfaction from causing pain in a female (or same gender).
That's getting way too deep into it---he may have been a pedophile but then again he may not have been a pedophile. He might have been taking whatever anger, rage or agression he was feeling about other areas in his life out on this baby. Because she was safe to do it to, she was smaller, weaker and defenseless.
These crimes are so psychological they give me the ebbie jebbies and I don't delve too deeply into sex assaults of children. It's not something I can handle well.
JMHO