The fact that they were the Mayor and Police Chief of Baltimore, and thus the government officials responsible for controlling the city's bridges and roadways to prevent rioting.
Bump!
But the bridges weren't in the City of Baltimore (unless you believe city limits stretched almost to the Pennsylvania border), and they were quite likely owned by the railroad.
"To effect this it was decided that railroad bridges north of the city should be destroyed. When word came that night that more troops were to enter Baltimore via the Northern Central Railroad, and that there was a possibility that some troops had already arrived at Perryville, where rail cargoes were ferried across the Susquehanna, the board decided to act. Marshal Kane was sent to see the Governor, who was staying at Mayor Brown's home. Kane informed Governor Hicks that within a few short hours a large body of troops, no doubt aware of the day's events and inflamed with resentment, would enter Baltimore. The Governor, though he would later deny it, supposedly gave his permission to burn the railroad bridges of the North Central and Philadelphia, Wilmington & Baltimore Railroads, effectively cutting Baltimore off from the North.
"Marshal Kane returned to the office of Charles Howard, president of the police board, and informed him of the Governor's consent. Necessary orders were given and messengers were sent out into the night to collect the men necessary to carryout the operation. One such messenger arrived shortly after midnight at Ravenhurst, the beautiful Victorian home of Isaac Ridgeway Trimble in north central Baltimore County. Trimble was Superintendent of the Baltimore and Potomac Railroad and a Colonel in the state militia. The messenger who awakened him presented Colonel Trimble the following order:
"Baltimore, 20 April 1861, 12 1/2 A.M.
By the authority of the Governor of Maryland and for the protection of the City of Baltimore, I hereby direct Col. Isaac Trimble to proceed up the Philadelphia R.R. and break down the bridges thereof up to the Susquehanna River, and also require all persons to refrain from opposition thereto.
George William Brown
Mayor of Baltimore"
(1) The Mayor of Baltimore is ordering that railroad bridges be burned north of the city, up the the Susquehanna River in northeast Maryland, near the Pennsylvania border - not exactly in his jurisdiction.
(2) The Mayor claims sanction by the Governor, who denies it.
(3) Even if the Governor did sanction burning the railroad bridges, it was an illegal order. Unless Maryland is the exception, the bridges are owned by the railroad company and are private property.
(4) The bridge-burning was a military action.