> Can you sue the CIA for civil damages if it killed one of your
> relatives?

Almost never.

[Governmental immunity][1] (a.k.a. sovereign immunity) bars most suits for intentional use of force by the government that is legally authorized by a government official with the authority to authorize this action under the relevant statutes, regulations, executive orders, and chain of command.

The [common law state secrets privilege][2] bars a very large share of the remaining cases, such as most killings arising from negligence in the course of covert operations, and most legally unauthorized killings by covert operatives.

There are narrow cases in which one case sue for a violation of civil rights in such a killing (under several statutes, the most famous of which is [this one][3] applicable to state and local government officials, which has a federal law enforcement counterpart), but usually, if a national security justification is advanced, the much narrower standard of relief applicable to combat killings and collateral damage in war (subject only to criminal war crimes review rather than civil liability) rather than the 4th Amendment analysis applicable to civilian law enforcement intentional killings by the government, applies.

Of course, if the CIA negligent kills someone due to negligence in connection with its non-covert activities (e.g. a non-covert delivery truck delivering ordinary paper gets in a deadly traffic accident caused by negligence en route to CIA headquarters), the person killed may sue the U.S. government under an exception to governmental immunity provide for in the [Federal Tort Claims Act][4] which would be brought in the U.S. Court of Claims (generally in a non-jury trial with more limited damages available than in a private automobile accident case and with more involved procedural requirements).


  [1]: https://en.wikipedia.org/wiki/Sovereign_immunity_in_the_United_States
  [2]: https://en.wikipedia.org/wiki/State_secrets_privilege
  [3]: https://libguides.law.umn.edu/c.php?g=125765&p=2893387
  [4]: https://en.wikipedia.org/wiki/Federal_Tort_Claims_Act