The announcement came less than one month after the death of Freddie Gray, a 25-year-old black man injured in police custody, sparked outrage in Maryland's largest city, although the department's wider investigation is not specifically tied to his individual case.
A Justice Department statement said the investigation will focus on use of force, including deadly force, by officers, as well as stops, searches and arrests.
"Ultimately, this process is meant to ensure that officers are being provided with the tools they need - including training, policy guidance and equipment - to be more effective, to partner with civilians, and to strengthen public safety," U.S. Attorney General Loretta Lynch said in a statement. (Reporting by Lindsay Dunsmuir and Susan Heavey; Editing by Bill Trott)