The explosion flame on the boats at the beginning that kills the officer is obviously superimposed. The flames look like a film put over the actual image. Only the smoke coming from behind the stack of boats is not superimposed.
When leaving the police dept. to ask the murdered officers "roommate" some more questions, Mike, instead of calling out to his new partner by his correct name of "Dan" calls out to him by the name "Stevie", his previous partners name.