The picture of the 12th Precinct is different than it's been in past episodes.
The nose says the killer had the odor of nail polish remover, to which Castel responds, acetone, then goes on to say Freon smells like acetone. There are actually two errors in this exchange. First, Freon is odorless and colorless, so it does not have an odor. Second, Freon is volatile (volatile: something that evaporates rapidly) and would rapidly evaporate leaving behind no residue of any kind.
Ryan's ":accidental" shooting of Esposito should have resulted in an AI investigation and a Shooting Review. Basic firearm discipline requires that one verify the target before firing. The shadowy figure Ryan saw could have been anyone, and the use of lethal force against a suspect is very tightly controlled by law.