So you promise the man, he hides behind a bush and you keep walking.
Ten seconds later four men turn the corner where the panicked man had come from and head towards you. As they get closer you see that they are, indeed, police officers. They walk up to you and ask if you have seen the man they were chasing. What do you do? Do you lie? Why?
In America we begin with a presumption of innocence. What matters most in Jewish law, however, is the preservation of innocent life. Virtually all obligations and prohibitions may be suspended in order to save a life. That concept, known as pikuach nefesh, can guide us here.