Re: Shooter loses registered silencer to police.
It's going to be a simple case. The prosecution will try to prove that they were using the suppressors. The defense will try to prove that they were not using them. The judge/jury will decide.
The idea of a law enforcement officer being in violation of the NFA for seizing a suppressor is ridiculous. If the OP has the facts right, there was plenty of probable cause to seize the suppressors.
If at first you don't succeed, shoot, shoot again.