My guess is, P.O.W., or a hostage. Since hostages were typically children of conquered tributary rulers, they'd be killed, but given a decent burial. Elam went through at least three capitals, struggled for control over Mesopotamia (Kudur-Laghamar being the high king "Chedolaomer" mentioned in Genesis), and eventually vanished under more or less foreign control.
Most interesting.
Could the gag have been to keep the mouth closed, sort of the way a headcloth was used to keep the mouth from hanging open?