DS9 Season 1 Episode 18 Duet

Plot

A freighter docks at Deep Space Nine so one of its passengers may receive treatment for a condition called Kalla-Nohra, which was caused by a mining accident at a brutal labor camp called Gallitep during the occupation of Bajor. As the patient is a Cardassian, Major Kira has the man arrested as a war criminal, only to find his name, Aamin Marritza, is not listed for any crimes. Station commander Benjamin Sisko sees no option but to release Marritza, but Kira is adamant - Marritza is a Cardassian who was present at Gallitep, which is reason enough. Sisko decides to investigate further and has the man held in custody. Citing a conflict of interest, Sisko asks Kira to remove herself from the case, but her emotional plea and a promise that she will remain professional convince him to let her continue. When she interrogates Marritza, he says that he was only a file clerk at Gallitep.
A photograph from Gallitep reveals that the man being held is not Aamin Marritza but Gul Darhe'el, the "Butcher of Gallitep" who reportedly murdered thousands of Bajorans. When confronted with this information, the prisoner proudly admits to being Darhe'el. Kira is shaken. Darhe'el seems convincing; however, inconsistencies in his story begin to stand out. Gul Dukat, the Cardassian former prefect of the occupation, asserts that Darhe'el is dead – his funeral was widely attended, and half of the Cardassian population viewed his body in state. Furthermore, Darhe'el was not at the mining camp on Bajor during the Kalla-Nohra disaster and thus could not possibly have the syndrome. Dr. Bashir discovers that the prisoner has undergone cosmetic surgery, leading Kira to realize that he is indeed Marritza, but is deliberately impersonating Darhe'el.
Kira confronts the prisoner with this information. Marritza eventually breaks down in tears, branding himself a coward for not attempting to stop the atrocities at Gallitep. He begs Kira to prosecute him as Darhe'el, as he intended all along, insisting that Cardassia must be forced to admit its wrongdoings and Bajor must have the satisfaction of successfully prosecuting a Cardassian war criminal. Kira releases Marritza, realizing he is a good man so traumatized and remorseful from his experiences that he would give up his life to make amends. Kira escorts Marritza to a ship departing from the station. On the way out of the Promenade, Marritza is suddenly stabbed to death by a Bajoran. When Kira demands to know why, the Bajoran echoes her earlier sentiment: that being a Cardassian is reason enough. Kira, having had a change of heart, asserts that it is not.