The so-called Munich massacre changed the Olympics forever. "A political terrorist attack at the world festival of peace and international collaboration was unprecedented--and sacrilegious," says Olympics historian John MacAloon.
http://www.usnews.com/usnews/issue/040614/misc/14olympics.b.htm

Security was lax at the 1972 games by design. Hosting the summer Olympics was Germany's chance to show the world that it had redeemed itself from Nazism."Security personnel were told to go easy, not to be gruff or dictatorial," says Olympics historian Allen Guttmann.

Because much of the roughly 20-hour crisis was broadcast around the world, Munich was "the most consequential terrorist incident in history prior to 9/11," says Rand Corp. terrorism expert Bruce Hoffman.