I haven't seen it, but do they explain why they need somebody to kill people they drop through time and space? They've got a sheet laid out in a corn field, so obviously they can control precisely when and where the person shows up. Just teleport them over an active volcano. Or onto the deck of the Titanic. Or in one of the towers on 9/11. Or on the Faroe Islands in the height of the Black Plague. Or a hundred feet under the surface of the ocean. Or to the moon.
"The trouble with being a ghost writer or artist is that you must remain anonymous without credit.
If one wants the credit, one has to cease being a ghost and become a leader or innovator." — Bob Kane