I would love to know how to confirm Tony's information. I have been searching books and online ever since you posted the question to find a definite answer. The trial transcripts, of course, don't give you the vote make-up. So far, the closest I have come was Kauffman's American Brutus, where he specifically gives the votes against Arnold, O'Laughlen, and Mudd as 5-4 and those involving the death penalty as two-thirds majority. In the case of Spangler, however (like everyone else!), Mike just says, "He received a six-year sentence."
My guess is that, if you were guilty of anything, the vote was 5-4. If you deserved to die, it was 6-3. If by any slim chance there had been someone declared innocent, the vote would have been 4-5 or less???