One glaring problem

While this detective drama/thriller with George C. Scott and Marlon Brando has a convoluted story, it can (sorta) be followed if you utilize the subtitles, which helps you keep track of all the names and so forth. The filmmaking is top-of-the-line for the time period (1980) augmented by the WW2 embellishments and the mix of Los Angeles & Germany/Switzerland locations.

One glaring issue, however (SPOILER), is how practically every key person detective Caine (Scott) questions gets shot afterward (even if not immediately), which becomes predictable and eye-rolling as the film proceeds.

Furthermore, why are they being shot? Is it because they dared to talk, which is the presumed reason? Or were they being eliminated after fulfilling their purpose in a wild goose chase? Are the masterminds behind the shootings just trying to discourage Caine? If so, why not simply shoot Caine (which, admittedly, they seemingly try to do outside the Berlin zoo)? Everything seems to be explained at the end, but I'm still trying to put the pieces together.