An after-the-fact event; held

Hello,

Three hours and forty-three minutes into his shift on his first day as a sworn officer, he'd gotten a call to a convenience store. Robbery in progress. [...] It was obvious when he'd pulled the squad car to an abrupt stop in the convenience store's parking lot that the robbery in progress was now an after-the-fact event. A half-dozen people, some crying, milled around outside the store.

(Quoted from Alone at Night by KJ Erickson.)

1. What is an after-the-fact event? In the context, does it mean that the robbery was already over?

If yes, can I say
"the midterm exam was now an after-the-fact event"
to mean "the midterm exam was over"?

Everything [the witness] told [the officer] held. They arrested the shooter in less than twenty-four hours.

(Ibid.)

2. What does "held" mean here? Does the first sentence mean that everything the witness says is of great use? Or, is a "true" omitted after "held"?

Best Wishes