Credit to this info goes to ZELLGODDESS who posted this Tip in the Quest info. Just reposting it here, since it's relevant to this item.
This shirt comes from Iceberg the bear, who roams Everfrost Peaks in the plains (tundra) area. Iceberg is Tundra Jack's pet bear. If you feed Iceberg a "Lion Delight", he will cough up this "Sweaty shirt".
If you cast Identify on the "Sweaty shirt" it will say "Item lore: Murderer's Shirt"
Bordering the plains area is a wolf named Snowflake and a few other barbarians standing around. Snowflake is good at tracking things. You can say stuff like "where's megan" and she'll go "ruff ruff woof" and track down Megan. Very amusing. Apparently if you give this shirt to her, Snowflake will sniff it, and then track down some murderers.
Be prepared to kill these murderers. Then loot their heads, and... give the heads to "the questgiver".