Albert Barnes Commentary Leviticus 19:16

"Thou shalt not go up and down as a talebearer among thy people: neither shalt thou stand against the blood of thy neighbor: I am Jehovah." — Leviticus 19:16 (ASV)

Stand against the blood of thy neighbor - Either, to put his life in danger by standing up as his accuser ; or, to stand by idly when your neighbor’s life is in danger. Whichever interpretation we adopt, the clause prohibits that which might interfere with the course of justice.