Infiltrator (The Pitt)

The Infiltrator is a scoped, silenced assault rifle that will be added to Fallout 3 with the release of The Pitt downloadable content pack in March 2009.

It is dropped by the last enemy you must fight in the fighting arena of The Pitt, The Arena. You must fight three slaves in order to gain audience with Ashur, but you must kill each before succumbing to radiation poisoning. After defeating the third and final enemy, he drops the Infiltrator, you get a new perk which raises your resistance to radiation, and you will have completed a quest, gaining an achievement.