do you know this movie,villain jumps out the window wrapped in the American flag

Some guy murders a woman in an elevator

bunch of punks invade an office building an take hostages

at the end the main villain jumps out the window wrapped in the American flag

some broken down ex-war hero who has a lot of dialogue in his apartment is the hero

Its old(early 80s maybe), low/medium budget an violent


Thanks if anyone can help