What in the world is the legal reasoning behind this??
The majority of the occupiers seem to have been confidential government informants who may have been responsible for supplying the firearms, and the prosecution refused to have these people identified and take the stand. Thus there were due process and entrapment concerns plus technical issues with the definitions of the crimes they were charged with.
Wait, this is like how most neo-nazis in Germany are government informants? Heh, that's funny if true.