A trained assassin like Ziva David said that a "silencer" was used to kill a character. Even with English being a secondary language she would have said "suppressor".
Tony tells Ziva she should say "job at hand" when she says "job in my hand". Ziva is more correct here: she is holding the piece she is working on, so it is "in hand". To say that an operation is "at hand" implies that it is underway, or about to become so, but not necessarily physically in touch. There may be several jobs "at hand", but only one "in hand" at any moment.