Theoretically they could have knocked the door in if they had a search warrant. So maybe the FBI has a quik-pik set they use to stealthily enter after whispering "FBI. We have a warrant. Open up." That way they might catch suspects off-guard. I'd be surprised if the agent didn't testify that there was no response to their verbal command.
If these were the WLs skippy/Stry walnut sauce emails it could be an epic trolling of these monsters also.