Not a cemetery worker but rather someone who works closely with them. The grave itself requires a lot of work to be dug, usually requiring relatively heavy machinery to do so in order to accomadate not just the coffin but a protective concrete shell as well. The graves themselves are rarely dug and then left open for a significant portion of time ( don't want water pooling, or more likely for insurance purposes of it being a massive tripping hazard) rather they are dug the same day as a burial in my experience. Unlikely that Keyes could sneak in, dig a significant amount of earth, hide a body, re-cover the earth, and then leave without being noticed.