I'm kind of fixated on the slab search. You don't go to that much trouble without a good reason. The technology to look deep into the earth (or under water) for both forensics and anthropology are advancing at a rapid pace. Putting a body in the water, in the ground or even under concrete are virtually not an option anymore. If LE has at least a basic idea of where to look, they are most likely going to find it. Drones, Underwater ROV's, GPR, Lidar, Side Scan Sonar, ERT, ERI, deep seeking metal detectors, LABRADOR and the list goes on.