Travel to Turmoil Cemetery in the The Commonlands. There, two lost souls spawn; these are the placeholders for the Graverobber, the mob that must be killed to update this quest. He spawns at ( -1313, -69, 344 ) /waypoint -1313, -69, 344. He spawns close to 3am game time.
Note that the Graverobber is a rare spawn; though many will say that he can only be found at night, he may be spawned at any time of day -- simply keep killing the placeholders.
11/07/10: Killed the placeholders a few times each and the Graverobber spawned around 9:30am Norrath time.
19 December 2010: Killed the placeholders several times during the night, but the Graverobber didn't spawn until 3:00 AM Norrath time.
21 Sep 2011. Took me 3 times to clear the placeholders. Ingame time: 6:30