Nude, suffocated, seven year olds do not turn up in trash dumps through accidents or natural events.
Since seven year olds have no legal ability to consent to any actions done to them, any events leading to her death are the sole responsibility of the person acting upon her, and with greater expectation of intentionality as all adults are expected to act in a manner as to protect children from harm.
Premeditation in this case of a murdered kidnap victim is implied in the act of kidnap. The only defense against the charge of murder in a kidnap case is the return of a live victim. Once a kidnap victim is found dead, it is automatically felony murder. The law is very harsh with kidnapers, has been since the Lindbergh kidnaping.