From Halopedia, the Halo wiki
Pitiless was a Covenant vessel operated by Kig-Yar. During or before 2524, the High Prophet of Restraint ordered all Kig-Yar vessels to be searched by squads of Sangheili and Unggoy after the Pitiless was found with "an Unclean being's" corpse aboard. This corpse was likely that of a human, as the Covenant are known to refer to humans as "Unclean".
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