Leviticus 19:16 "Neither shall you stand idly by the blood of your neighbor"

We are not allowed to stand by and refrain from saving someone's life if we can possibly do so.

We must do everything we can to help him.

This Negative Mitzvah also includes our obligation to give testimony.

We are cautioned not to avoid serving as a witness if we have seen or know of something that can effect the outcome of the trial. We must always help a fellow Jew protect his possessions and his life.