Excerpt from the link to which akenaton refers:
"Your intention, but for your apprehension, was to attend a real camp and to use real guns in training at that camp..."
I would read this "but for your apprehension," as "but for the fact that you were apprehended (caught)".
It is common that if a criminal is apprehended during the planning of a crime that charges be brought. ie, that conspiacy to commit a crime, is in itself a crime.
(1) I don't know what evidence there was, that these men planned to do something illegal.
(2) I am not a lawyer or paralegal of any sort.
I just think that the word "apprehension" may have been misunderstood.