Baltimore police have enlisted state troopers to help patrol high-crime areas of the city in recent months, a move that represents a new cooperation for two agencies that have historically been at odds over the state force's role in local law enforcement.

Though troopers have had a presence in Baltimore for decades as part of various task forces, under state law they can only police the city when invited by the Baltimore police. Discussions about whether state police should have jurisdiction here have previously been held up by disagreements about the scope of their power.
Maryland state troopers helping Baltimore City police patrol high-crime areas - baltimoresun.com