My take on how this works, in summary: he distributed something totally unrelated to some people, quite a few of them, not even friends probably, with the instructions to do some non-specified action with that thing if something bad happens to him. Those non-specified actions on those non-specified things, once done together by a minimum number of different actors, act as the famous dead man switch, which is therefore impossible to intercept via MITM attacks and impossible to beat,even by torture, because every actor could only know his/her specific action. For what we know he could even have "outsourced" the whole setup to someone who then fleed/changed identity, this way not even him may be able to tell what actually has to happen in order to trigger the release of the documents.

[edited for clarity]