[DoodleDawg]

I believe there multiple arrests, including of city officials, that preceded the arrest of legislators.

But during the same period, September 1861, long after the rebellion had begun.

[Sherman Logan]

Nope. The mayor, chief of police and other city officials of Baltimore were arrested it mid to late May.

This was in response to MD sedition and attacks on US troops and transport systems, not to some supposed CSA invasion. Although people might have been paranoid enough to think the CSA was coming.