When Nick is interrogating Richard O'Malley he says that O'Malley stuffed a rag between the catalytic converter and the firewall. Catalytic converters are not located in the engine compartment, they are usually located on the exhaust pipe before the muffler underneath the car.
at 23:31 when Warrick pins a suspect to a wall, he is wearing sunglasses, as he is pinning the suspect though his sunglasses disappear then reappear then disappear again when he talks to the suspect.