According to this article, Collings claimed he acted alone. He said he took the girl to the sinkhole in his truck. The problem with that story is that the cadaver dogs kept hitting on Spears' mother's vehicle.
Perhaps Collings confession was prior to and with no knowledge that Spears also confessed. Wonder what possible motive Collings would have to protect Spears. Perhaps the notoriety and not wishing to share the spotlight?