After World War II, Germany was all about fun and care-free feelings that translated into low security for the 1972 Olympics. The West German Olympic Organizing Committee had encouraged an open and friendly atmosphere in the Olympic Village, to help erase memories of the militaristic image of wartime Germany and, specifically, of the 1936 Berlin Olympics, which had been exploited by Nazi dictator Adolf Hitler for propaganda purposes. Security in the athletes' village was intentionally lax and athletes often came and went from the village without presenting proper identification. The officers dressed in light blue, weren't armed. Many athletes bypassed security checkpoints, and climbed over the six-foot chain-link fence surrounding the village. David Berger, one of the killed athletes, had a younger sister who used his Olympic jacket and snuck past security to see him.
The absence of armed personnel had worried Israeli delegation head Shmuel Lalkin even before his team arrived in Munich. In later interviews with journalists Serge Groussard and Aaron Klein, Lalkin said that he had also expressed concern with the relevant authorities about his team's lodgings. The team was housed in a relatively isolated part of the Olympic Village, on the ground floor of a small building close to a gate, which Lalkin felt made his team particularly vulnerable to an outside assault. The German authorities apparently assured Lalkin that extra security would be provided to look after the Israeli team, but Lalkin doubts that these additional measures were ever taken.
All of the research I have come across points to lackadaisical and insufficient security force at the Munich games, especially around the Olympic Village. However, Avraham Melamed, an Israeli team member, refutes that statement emphasizing that security was present, more than he had seen at either of the 2 previous Olympics he attended (Tokyo in 1964 and Mexico City in 1968)