Two inmates in Sioux Falls wrapped plastic shrink wrap around a 63-year-old guard's head, took his uniform and left him to die, the Pioneer Press reported.
Eric Robert and Rodney Berget, both 48, used the guard's uniform in an unsuccessful attempt to get past security, according to the Star Tribune.
The two inmates were charged with first-degree murder.
They are being held without bond.
Robert was wearing the uniform and pushing a cart with two boxes on in, where Berget was hiding inside.
When Robert failed to swipe his electronic ID card when exiting an area, officers became suspicious and called for more guards.
The two inmates are not allowed contact to each other.