The government probably has evidence, maybe or maybe not persuasive enough for a conviction. That evidence will be presented in due course, not all up front to the media.
Given the circumstances, the government absolutely does have an obligation to present its evidence up front. You cannot use federal agents to arrest officers of a state government unless the charges are rock solid. There is a strong public interest in this case and the current administration has shown that it is owed zero deference or presumption that it is acting in good faith.
That's my problem: while the arrested person is already forced the humiliation of being arrested, having their freedoms stripped from them, they have no remedy and have to wait in the state of being humiliated while the government who prosecutes them isn't also restrained or humiliated during the wait to present evidence.
And additionally, there have been several recent prominent cases where the government has failed to produce any evidence in court while publicly saying to the media that they're arresting criminals-- of course, the government is able to access the media to claim this while the people they've arrested who, again, have had their freedoms restricted while the people who restrict them are under no similar restraint are unable to do the same!
We can see this in action right now: the government gets to claim to the media that the judge is obstructing arrests of illegal immigrants, while the judge can do no such media counterclaim and has to wait in restraints.