I'm pretty sure his 'documentation' are quotes from Jefferson himself.
Jefferson's personal beliefs changed and were distilled throughout his life, so there is a bit of conflicting information out there, plus he was a politician so some of his quotes were in that context (i.e. saying what he needed to say, to whom, at a specific time, in order to achieve his aim).
It's simplistic to call Jefferson a Deist, but for shorthand, that's pretty close.
Look, we can argue Jefferson for months, but for me the important point isn't whether Jefferson believed in God (he did), or whether he believed in the Bible's version of Jesus (he didn't), or whether he thought the baseline message of Jesus' teachings, aside from the miracles, was the proper moral code on which we should dedicate our lives (he did).
The point, for me, is that Jefferson was highly suspicious of the intersection between Church and State.
Jefferson coined the phrase, "a wall of separation between Church and State".
Believe whatever you want to believe in terms of religion, but separate that from our civic government, and we will all prosper.
Once government starts getting into questions regarding religion, that's when the clusterpuck starts.
Freedom of religion, freedom from religion, etc.