Complex sentence: The Glatzel family, along with the Warrens, then proceeded to exorcise David, a process that dragged on for several excruciating hours, and only concluded when the demon fled the child's body, supposedly taking up residence within Johnson instead.
Split into simpler sentences: The Glatzel family, along with the Warrens, then proceeded to exorcise David. The process dragged on for several excruciating hours, and only concluded when the demon fled the child's body, supposedly taking up residence within Johnson instead.