What is the liability of an individual who restrains a person when they do not know the killer's intent to execute the captive?

Primary text

If the retainer did not know that the killer intended to execute the victim, then nothing is incumbent upon the retainer. This is because the retainer is an indirect cause (mutasabbib), while the killer is the direct actor (mubashir), and the effect of the indirect cause is voided when combined with direct action.