Police spokesperson Angela Cruz said the incident was called in just before 12:30 p.m. on Monday from the Library, at 4201 Knowles Ave. in Kensington.
Cruz described the suspect as a a black man in his 60s with a tall to medium build, beard, red top and red pants. Cruz said a preliminary report on the incident classified it as indecent exposure.
The police lookout was for a man seen masturbating next to a patron inside the library.
Flickr photo via Montgomery County Public Libraries