In tort law, generally speaking, the law only holds a person responsible for his or her own actions. Restatement (Second) of Torts §315. The reason for this is clear: If the purpose of tort law is to influence behavior, the law only ought to be enforced where it acts as a deterrent against bad behavior. Usually, a person has not participated in bad behavior where a third-party actor has behaved poorly. It is thus perfectly sensible that tort law does not hold a person responsible for the actions of third parties.