The Argrathi are a species from the Gamma Quadrant. They use advanced mind altering techniques to implant false memories of imprisonment of those they arrest and charge with crimes.
The Argrathi had begun to visit the Alpha Quadrant by 2370. In that year, B'Elanna Torres thought a sick woman on Dalgren looked Argrathi, due to her plump face and high forehead. (TNG novel: Quarantine)
In 2372, Kira Nerys and Miles O'Brien visited Argratha. O'Brien was curious about their technology and was arrested by Argrathi security forces and charged with espionage. O'Brien was subjected to twenty years of false memories, including killing his cellmate Ee'char. (DS9 episode: "Hard Time")