Apparently the state highway people built a new concrete bridge some distance from the truss bridge and left the old one stand (historical concerns...). That took the old bridge out of service. I would guess that the brothers then took apart the truss work leaving the deck and support beams for last (safe since the bridge no longer carried traffic loads). After removing the wooden deck they probably dropped the support beams one at a time (torch cut the ends off or yanked them off the rip-rap abutments with a wrecker)and then skidded them out of the river with the same wrecker (I would have rigged a block up a sturdy tree on the shore so the angle of the winch cable would keep the end of the beam from digging in). I would expect that they cut all the structural steel into convenient chunks to expedite transportation.
Wisconsin has several post and beam (typical old wooden barn construction w/ pegged joins) covered bridges which are out of service with a nearby steel bridge carrying the traffic. The old wooden bridges are interesting to walk through and study the construction. Pity those guys got greedy. They were probably turned in by the people they approached to sell the "salvaged" steel. Metal recyclers are getting pretty savvy about their customers. If they don't know you and you show up with a lot of metal they get suspicious really fast.
Regards,
GtG
I think such a project would be an all or nothing project for thieves.
You could take down one support and sell it but then you would never dare go back because your theft would have been discovered and the bridge would be watched closely for some time.
If they knew the bridge was still occasionally used they would know that they would have to be fast to escape observation dismantling the bridge.
You could not take down the bridge and hide the metal some where because it would be to large an amount to hide and if discovered the authorities would be watching it to see who came for it and you would be arrested the moment you showed your face to load some up to sell.
Such a theft is all or nothing unless all you want is a little beer money.
Perhaps they needed to find a known crooked recycler. (If that is how they were discovered).