WASHINGTON — Police in the nation’s capital say a contractor working on the Frederick Douglass Memorial Bridge has been stabbed to death.

Police Chief Peter Newsham tells reporters that 62-year-old Robert Bolich, of Alexandria, Virginia, was attacked Thursday afternoon on one of the bridge’s pedestrian walkways and pronounced dead at a hospital.

The police chief said authorities didn’t yet know the motive as of that afternoon, but a suspect was arrested at the scene. Police later announced that 42-year-old Lance Ammons, of no fixed address, was being charged with first-degree murder while armed in the attack.

Authorities didn’t immediately release additional details about the case. It’s unclear whether Ammons has a lawyer.

Bolich worked for HNTB Corp., a construction management firm. Spokesman Christian Munso says HNTB is cooperating with authorities.