#1 - Aug. 17, 2012, 4:03 p.m.
Blizzard Post
With the advent of area looting (AoE looting), it has become difficult for addons to determine what creature dropped which item. In order to help authors with determining creature drops, we have added a function that will return the creature GUID, along with the count, for any item in your loot window.

GetLootSourceInfo(slot) - will return a list of creature GUIDs and count.