One question about the ending

The detective was looking into the Adam as a possible suspect. Remember she learned the shooter from the beginning worked at the college he went to. All the coincidences were setting off red flags for her. She wanted to let the wife know that the case was closed and he was not a suspect (possible criminal).

** SPOILERS BELOW ***

The detective suspected Adam was crooked (YOU'RE probably supposed to assume she's racist because she's white and works in law enforcement) and was involved in the diner robbery. It's just too much of a coincidence when one person is loosely connected to 2 deaths. It would've been more clear if she could've been seen talking to someone else at the Police station about her suspicions, rather than just hitting Katie with a bunch of questions about his usual patterns at the diner.

The entire diner scene, Adam's possible connection to the hold-up, him as a possible murderer, was all a red-herring so that you falsely suspect he's the villain all along and get fooled.

And then when the money shows up gone at the bank, you're supposed to jump up and say "I knew it was him!"

(I knew he couldn't be guilty because it's not politically correct in 2020 to make young black guys killers anymore. )

Then at the end when he's innocent, you think "oh they fooled me, what a great plot device!".

Her suspicion is why she didn't like Adam, and why she told Katie "I know none of this is your fault". Plus she just liked Katie. I mean c'mon, Camila Mendes is a total cutie-pie !!!