Prevalence of child murder?

More and more little girls are being killed

I seriously doubt that that is the case, especially since IIRC violent crime is continuing on a downward trend, but I would of course be open to statistical evidence to the contrary.

As for the rest of your post, it is a tough time to be a pedophile. Little white girls getting killed has always been big news, but now that the media has a well-established narrative for the "dangerous predator rapes and murders little girl" cases, anything that fits it will shoot to the top of the headlines. Even if the victim was 17 years old.

Given the current climate and the constant "pedophile=monster" message shoved down all our throats, I could see how a pedophile with no means of emotional support could very well "snap" and break the law. However, I still think that a situational offender would be far more likely to kill a child than a pedophile would, even if he/she had gone off the deep end. Just a gut feeling here. These sorts of cases are pretty rare and we're unlikely to get an unbiased assessment of the killer's mind, so we will probably never know.