If they had gone out and gotten a individual court-order for each single citizen...then they might have a legal basis...but some blanket action like this? Its purely illegal and will wind up in court. My suggest for any citizen of Oshkosh who lost their weapon...don't take this into a lawyer...take it to small claims court and do it yourself. You don't need tens of thousands for this action. If 100 owners go into small claims court, and collect $2k each...they will have made their point and the cops will be out of $200k. Its fair and keeps the lawyers out of the mess.
The small claims will at best be able to get the gun back.
This whole mess sounds like another Houston K-Mart.