If people behave in such a way that you find it almost impossible to accept that they actually did it, then you can say that their behaviour was beyond belief.
An belief idiom dictionary is a great resource for writers, students, and anyone looking to expand their vocabulary. It contains a list of words with similar meanings with belief, allowing users to choose the best word for their specific context.
Wörterbuch der ähnlichen Wörter, Verschiedene Wortlaut, Synonyme, Idiome für Idiom belief