The accounts of batf, fbi, hs, all showing up make me wonder.
A local problem is LOCAL. let the police handle it at the start. In this case they should ask for help from sheriffs, other towns, texas rangers, but it is theirs. The investigative forces can come in later.
In reality sheriffs only are the elected law.
Side note; the local metro area has a dozen police forces, each with a swat. The metro college, city college, state university all in the core city also have a swat. Do you really think the city will not send in their armored car if needed?
That indiana mall shooting shows the up side of a competent citizen with a gun. And he did not do a barney fife and try to clear the perps gun. Last year another scenario got the good guy killed because he did not quit handling guns.