Boy that's nice. Searching your belongings with no evidence you are involved in a crime other than possesion of a tool that thousands of others have. These federal judges sure know how to use the Constitution as toilet paper. I sure hope no one shoots anyone with a 5R barrel.
The FBI obviously knows which Makarov (East German, Russian, Bulgarian etc.)that was used in the crime. They also know that it had a .380 conversion barrel. They know to whom each and every one of these particular Markarovs were sold to for the first time. They also have a list of persons who purchased .380 conversion barrels. IMO the chances of recovering the actual murder weapon are zero and the FBI knows it. By tracking the transfers both private and through FFL dealers the FBI is obviously trying to connect one of these Mararovs and/or a .380 barrel to their prime suspect. This is why I always advised my customers to keep a record of who they sell or trade their guns to. You never know when the ATF or FBI might come a knockin'.