When Derek is first shown holding the large syringe, he is holding the needle up. When the camera angle changes, he is now holding it plunger up. But then for the rest of the scene, he is shown holding it needle up.
The victims faces are not painted to resemble any particular character from commedia dell'arte, all the actors wore black masks, with the lower part of their face bare (the "white" part).
Puncinella was characterised by his big nose, squeaky voice, acrobatics and being a charlatan. Not by being stupid and never speaking.
There's no reason to imagine the killer painted the victims faces while they were in the throes of an agonising death. Embolisms aren't the torturous way to die described by the ME, and even if they were, there was no need to paint the victims when they were still alive.
Not speaking did not make Puncinella the first mime.
Puncinella did speak, as did mimes. Mime is also a couple of millenia older than commedia dell'arte, originating in the 5th century BC.
Mime was simply a type of play. Usually a short play depicting scenes from everyday life, in which characters spoke and sang.
When Rossi and Morgan are talking with the SWAT leader in Baltimore, the tube for Morgan's ear piece keeps going from in his ear to out of his ear.