Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.

the tokyo subway sarin attack (subway sarin incident (地下鉄サリン事件, chikatetsu sarin jiken) was an act of domestic terrorism on 20 march 1995, in tokyo, japan, by members of the cult movement aum shinrikyo.
tokyo subway sarin attack