Plague Squad

"'They seem to be a virus, infecting scouts one by one.'"The Plague Squad was assembled by Henry Sullivan in 790, thought to be one of the foundational squads of the Scout Regiment. However, the squad soon became a toxic breeding ground for corruption.

The motives for the squad changed, becoming a guild of assassins working within the Scouts, killing anyone who was or would become a threat to Marley. They were forgotten and able to slip under the jurisdiction Erwin because of their sly methods of killing. Notable members include Jin Liu.

Plot
During the story, the Plague Squad is first introduced in the eighth volume of chapters for the manga, and the first episode of season three of the anime. When Jin transforms into a titan, the Plague Squad finds out and offers him a deal: he can join them, or be exposed and killed by the Scout regiment. Placing his life above other, he joins and hesitantly agrees to murder Kate, Jason, and Grace.