Question: Does Liam Neeson (Dr. Martin Harris) ever pick up a gun? And if so, when? I've seen him with a gun on posters and the DVD case, but I don't think I've seen him with a gun in the film.
Question: Why do they simply kill dozens of people in the movie, but with him it has to be something long and drawn out, like poison in the hospital or drugs in the parking garage?
Answer: Because the killers need to make Liam Neeson's death look accidental. The police think Neeson is crazy, and is not telling the truth when he claims Liz is his wife. The police simply think that Neeson is mentally ill and so dismiss his stories and allegations as untrue. However, if Neeson is then found murdered, there is the possibility that the police think Neeson might have been telling the truth, investigate, and foil the villains' plot. Therefore, Neeson must be killed to stop him investigating - but he must he killed inauspiciously, so it looks like an accident, so as not to make the police suspicious. Thus the poison in hospital - hopefully it would be put down as a standard non suspicious hospital death. And the drugs in the car park at the end of the film are deliberately mentioned by Professor Rodney Cole as being essential in making Neeson's death look an accident. Cole says that Neeson will seem to have killed himself with heroin and so will not consider his death suspicious. So basically these elaborate ways of killing are in order to make Neeson's murder seem an accident and so not make the police investigate.
Question: What (if any) is the significance of the "OZ" graffiti that pops up throughout the film? It became quite distracting as I thought it would pay off at the end of the film.
Answer: The 'OZ' sprayer is a very disturbed man who claims to be an artist but the courts think otherwise. You can found his OZ (which he claims to be read OLI!) everywhere in Berlin and Hamburg. It has absolutely nothing to do with the movie but you can't film a wide open scene in Berlin without taping it.