This is a very sad tragic situation for everyone involved. A 12 year old child disappears. The child's body is found weeks later. The police arrest her so called boyfriend, RM, and for now he is held in jail on sex related charges.
It is not unusual for the prosecutor to ask the court for a very high bond if LE has reason to believe that the person they arrested is a prime suspect in a homicide case.
One thing that we must remember here. Even if it turns out that RM didn't murder Kayleah, his troubles isn't over. In fact, it is only the beginning.
The prosecutor will still go after RM on the sex related charges. If RM is convicted, he will serve a prison term. The court can also rule RM to be a predator and force RM to register as a sex offender for the rest of his life.
It depends on what the evidence against him is (for example, was she pregnant or is it just hearsay) and who exactly the alleged victim for the charges was.
It may be that they suspect him in her death and the sex charges are a means to keep him in custody for the time being. We will have to wait and see.