This achievement must be done on the map "Five" which is unlocked after beating the campaign or using the cheat code: "3ARC UNLOCK".
- It can easily be done on solo. The map will start off with three Quick Revives in the open area for 500 points. it is best to knife the zombies and open up the door (750 points) and then clear the junk in front of the elevator (1000 points) and then build up 2750 points before reaching round 5. Once the player gets to the last zombie on round 4 (Note: it is recommended that the player keeps him alive until they are ready so it is best not to kill him now); the player should have around 2750 and then use the elevator (250 points) to the second level, and then go down the stairs and clear the junk there (1000 points) and make their way to the next elevator to clear the junk there as well (1000 points). Use the elevator (250 points) and head down to the third level. Run to the power switch and turn it on. Right afterwards, run back to the elevator and use it (250 points) and go back to the second level. Once there, go ahead and kill the last zombie. Now here is the tricky part; the player must stay in the elevator but DO NOT use it. The fifth round will start with a chance of him coming out, if not then the player must make it through this round, if the player gets downed at anytime in this round; the Quick Revive will heal the player, but the player will have to go back up to the first level and buy a second one. (Make sure to keep one zombie alive so the player can get back in place for the theif to spawn.) Once back in the lower second floor elevator; kill the last zombie. Once round 6 starts; the player will fight him, but to be safe; once the player hears a alert and the area turns faint blue; cook off a grenade and let it blow yourself up. Once the Theif spawns from the center of the second floor, unleash the solo's Quick Revive "Mustang and Sally" pistols (Pack-A-Punch M1911) on him and he will die in a matter of seconds and the achievement/trophy will be unlocked.
OR, play with 2 or more people, and have a Pack-a-Punched M1911 pistol. When the thief comes keep shooting until he dies. This can be a somewhat more diffucult way of getting the achievement/trophy ( this is due to how the player must ALWAYS have the Pistol with them ).
A detailed video which illustrates the above can be found: http://www.youtube.com/watch?v=yVe_I0lXZy0