How do you mean, did not have authority to? Assange was in Iceland at the time, and in Iceland there is a duty to assist people in distress. It is not unlikely

How do you mean, did not have authority to? Assange was in Iceland at the time, and in Iceland there is a duty to assist people in distress. It is not unlikely that Assange had some hint that something like what was done to people like Khalid El-Masri was going on, and it was through his acts that this was revealed. Such laws generally justify basically anything, provided that you have a reasonable suspicion that a person is danger.