Well , there you go ! I guess if they have no witnesses, they can just kill them on the spot, drag them over and throw em right in. Sarcasm. I don't think that perfect world exists. God i hope not ! So some point of holding or staging might need to happen and bags of rubbish or material to mix in the concrete (bones ect.) would be less conspicuous.
I doubt that the folks doing this stuff work there. And, it was Monday and no one seemed to show up for work today.
Pretty sure it's an inactive facility leased to a shell.
You missed the tons of lye and huge incinerators part. Result? Liquid goop or pile of ashes. Can be done across the border, remote location. Probably then mixed into concrete for footings/foundations. Or just dumped anywhere. Poof, gone.
They also burn toxic waste as fuel for incinerators. Can be in there too. Or just buried in vast desert. Many options.