They say they took the server for investigative purposes. If true, all they needed to do was take a copy of the disks. At worst the service might have been offline a few hours.

The purpose was to disrupt and stop the service with minimal effort and without having to wait for a trial. They were able to judge and punish a business without trial.

Why would they do that? In this case it might be the very common law enforcement motivation of doing something, anything.