Plot hole: Toward the end of the movie, it is revealed that Silvia spent the night in the secure room where the Matabo President was taken after the assassination attempt so that she could be alone with him and threaten to kill him. With the U.N. and Secret Service on alert for an assassination attempt, wouldn't they have swept the secure room right before the Matabo President arrived that day? In addition, Silvia would have had to use her access card to get in that area of the building, so there would be a record of her being in the building but not at her station. Wouldn't that raise some suspicion long before Tobin figures it out?
Plot hole: After the photographer is found dead in the bathtub, Sean Penn grabs the letter the photographer wrote to Nicole Kidman. He reads it to her in the park in English. Why would the photographer write the letter in English? He almost always speaks to Nicole in French, and if he wanted to keep the letter private he would have certainly written it in French.
Plot hole: There is simply no way that the United Nations would let Zumanie set foot into that building with an assassin still at large. Despite the movie's emphasis on his absolute need to be there that day or whatever, once a New York City bus blows up and the attack has ties to a soon-to-be visiting African leader's possible assassination, the U.N. should've been a ghost town.
Plot hole: After the explosion of the bus, Nicole Kidman is driven home by Sean Penn? No interview, no interrogation? She is a material witness with knowledge of details relating to the assassination of an exiled government leader and the deaths of over a dozen innocent bystanders.
Plot hole: At the end of the movie, Philippe tells Sylvia in his letter that Simon, her brother, was shot by a young boy. Philippe would not know this information because he was not in the soccer arena. Although he heard gunshots, there is no way that he knew that he was shot by a young boy.
Plot hole: When the Security chief is discussing the plan with the assassin, they are overheard by Nicole Kidman over the General Assembly microphones through a pair of headsets. Normally all this equipment is turned off when not in use to protect the system. The sound man had time to turn it off before he left even with an evacuation in progress. There was no way that the two were intending to be overheard either, as there was no way that either of them knew if, or when, anyone would be in the booth.
Chosen answer: At this point, she has set her mind on killing the African leader and knows she'll likely be killed immediately afterwards (police, bodyguards, etc). She's writing her name in anticipation of her death.