Either parties can file for a change of venue. Did one of the defendants use the mail in their home district to send anything of investigative value? Boom, jurisdiction. Bank in home district? Bank in another district?
Anything that was done to commit the crime can be used to set jurisdiction. You have to think really weaselly (I’m good at that;) I’m also really good at just making up words! )
blu, can you explain further. Very interesting.