The dilemma that Finch, Reese and Shaw face, whether to let McCourt live, causing the deaths of many, or to kill McCourt and potentially save many lives, is known in the field of Ethics as the Trolley Problem. The question is, you see a train speeding towards five people, who will surely be killed if the train continues, but can switch the train to a side track, on which there is only one person. In this case, is it ethical to switch the track, saving five lives for the price of one, or to let it continue, killing five, but saving the one.
The scene in the art museum where Senator Garrison meets John Greer, the triptych painting they are standing in front of is "The Garden of Earthly Delights" by early Dutch master Hieronymus Bosch (c.1450-1516), and it is located in the Museo del Prado in Madrid, Spain. The only Bosch painting in the National Gallery of Art is, "Death and the Miser."
Congressman McCourt buys the homeless man a meal at Ocean Grill, a seafood restaurant on the Upper West Side in New York. The restaurant's name is visible on the doors.
The opera Finch was listening to, and which the Congressman was to attend, is Il Trovatore (The Troubador) by Giuseppe Verdi. The opera was first performed in 1853, and is most famous for its easily-recognizable "Anvil Chorus", which is among the best known excerpts from any opera, and frequently used in film, television and advertising.