Is near a regulation stating it is a crime to do nil within the frontage of another crime?

If, for example, you stood and watched a murder happen, but did nought to stop it (when you were able to) can you be put to some extent to blame for the murder? I've heard there is a ruling in Britain like this, if at hand is, what is it called? Thanks x
Yes, it's called aiding & abet.

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