The case received attention earlier this month when the severed fingers of five of the men were sent to the U.S. military in Iraq.
Several relatives had taken the discovery of the fingers as a hopeful sign but hopes dimmed Monday when the FBI said the remains of Ronald Withrow of Roaring Springs, Texas, and John Roy Young of Kansas City, Mo., had been identified.
The other men still missing are Jonathon Cote, of Getzville, N.Y. and Bert Nussbaumer of Vienna, Austria.
Munns' mother said Tuesday that she lost hope that her son would be found alive after hearing that the remains of Withrow and Young had been identified.
"I think at this point, because they already killed the others, (he) is going to be probably dead as well, that's just a mom's intuition," said Jackie Stewart, a resident of Ridgefield, Wash.
Johnson-Reuben and Munns were guards for Crescent Security Group when men in Iraqi police uniforms ambushed their convoy near the Kuwaiti border on Nov. 16, 2006.