Why was Booth admitted into the presidential box?

[L Verge]

I previously mentioned a young researcher being interested in knowing about the structure of military trials. Here's the email I received from him this week:

Dear Ms. Verge,

Since becoming fascinated with Mrs. Surratt's story I have read numerous books, articles, documents, etc. and find the more I read, the more questions I have. The one that most interests me at present has to do with Military Tribunals. I have searched the internet and when that failed I asked a librarian at the local university and that failed. My question is what official guidelines, instructions, rules, etc. framed a military tribunal during the civil war? For instance, was the defendant presumed innocent, guilty or was this not addressed. Were judges given criteria such as beyond reasonable doubt to come to a verdict or not? By statute, what role does the judge advocate play? In other words are there some official, written rules that all military commissions must follow or are the rules for each commission left to the discretion of the commanding officer or judge advocate?

Any help with this will be greatly appreciated as I continue my research into this fascinating but tragic part of our history.

Comments or thoughts or flat-out accurate answers to any of the above?