Federal violations (crimes on federal property, some firearms violations, crossing state lines to evade capture, etc). The hostage situation need not be federal, but federal charges/investigation could have brought the feds there and the hostage thing just happened.
You'd be surprised that most things COULD be made federal. For example, you steal a candy bar from your local stop and rob. A case could be made, being that the candy was probably made in another state, that you just interfered with interstate commerce... FEDERAL CASE! There is no way that anyone woulod take this federal, just an extreme example.
Then there is the simple answer that we are often asked to help with non-federal cases.
We bring evil things to evil people, kicking in a door near you!
."In theory, there is no difference between theory and practice. But,
in practice, there is."
- Jan L.A. van de Snepscheut
"The difference between 'involvement' and 'commitment' is like
an eggs-and-ham breakfast: the chicken was 'involved' - the pig
was'committed'."
-unknown
Working on a PhD in CQB one doorway at a time.
When the wolf attacks, he will find not all who run with the flock are sheep!