If they seized the guns then they were seized either as evidence of or fruits of the crime they are investigating (unless they were contraband, say for example a SBR or full auto......or if they were an instrumentality of a crime of something like a murder). From what I gleaned from the story it looks like they think he was smuggling stuff from outside the country in order to add to his collection.
Oh.....and often, at least at the federal level, they won't file charges until the investigation is sorta at the end.
|