FYI on Stringfellow

[SSlater]

John, RJ, Steve. Great info and ideas, Thanx

I don't have any more to work with than you do, and our conclusions are similar. I will go a little further. to wit.
It appears that Stringfellow's assignment was to work out the details of the "Blow up the White House" scheme. His contact in the White House could provide a layout of the building and describe Lincoln's daily work habits. This would dictate where to place the explosive and the size of the explosive needed. In essence - it could be done.

There are many piece-meal scraps of info from others, at this same time, that indicates there were more people involved - such as the trips to New York, bits on more people "approving", or just "looking".
Booth was part of this planning and knew the schedule. So, when Harney was captured, Booth knew "it had to be done - NOW!" to get it done in the time-frame set in Richmond, so he acted.

Steve The "Copy" of the letter may not have include ALLthat was in the original, and needed to be destroyed, rather than force a new inquisition. (There was a reason the letter was destroyed).