In *Breaking Bad* Gus Fring told the Salamanca twins,

> The agent's name is Hank Schrader. May his death satisfy you.

https://www.youtube.com/watch?v=1yg44v6Qfqk&t=128

How did he know Hank killed their cousin, Tuco Salamanca?

The twins seemed to know only that a DEA agent killed Tuco, but they didn't know which agent until Sunset.

Only three people witnessed Tuco's death: Walter White, Jesse Pinkman, and Hector Salamanca. None of them would tell Gus at that time.

 - Hector would never betray the twins since they were his nephews, and to him, family was everything. On top of that, he and Gus hated each other so he wouldn't tell anyway.

- Jesse didn't have a trusting relationship with Gus at the time.

- Walter would never betray a family member, Hank, to a man he didn't trust, Gus.

If the only 3 people who saw Hank kill Tuco had no reason to tell Gus, then how did Gus know?