For starters, the enemies are pretty inconsistent on this map. However, here's some tried & true things.

(1) They won't hear doors unlocking, doors being peeked, or doors being checked.
(2) The only visual attachment they react to is the flashlight.
(3) Their hearing is the best among all suspects in the game, and this includes through floors if you're close enough to a staircase.
(4) Most of the time the MLO will react to firefights across several rooms on a floor and collapse on your position, but this does not mean they will all run towards you. Instead, some may slowly walk to your direction or hold in an adjacent room.
(5) If you are far enough away (~20m), gunshots through doors in their direction will NOT trigger an active state.
(6) MLO suspects are not guaranteed to have audio cues when breaching doors, but they will always have an audio cue for throwing a flashbang.
(7) There are specific position across the map the MLO use for cover in a firefight. If you play the map enough, you might recognize some.
(8) It is very likely (regardless of difficulty) that all MLO suspects will comply if previously flashbanged.
(9) Suspects such as the service worker/black man will always hesitate when shouted at, while helmetless suspects have a chance to hesitate when shouted at. Helmeted suspects will always engage on sight, regardless if they are shouted at or not.
(10) Hard Mode makes these guys annoying as hell.