Looks like he was indeed their next door neighbor. The suspect lived with roommates in #203 and the victim in #204:
Suspect allegedly blamed two Black men as key evidence led to arrest in murder of 11-year-old girl
He also apparently had family members in #206 and spent the night there after the crime (I guess trying to put as much distance as possible between himself and the crime scene before leaving for Louisiana shortly thereafter).
Everything he did - from where and how he hid her body, to what he did immediately after the crime - is indicative of how close he lived to the victim/scene.