These armed National Guard troops were sent to put down disturbancesin Baltimore, May 9, 1968.
Police advance toward protesters as a store burns, April 27, 2015, in Baltimore.
Patrick Semansky/AP Photo
A man is carried away by police during riots in Baltimore, 1968.
Baltimore police officers detain a demonstrator in the city on April 27, 2015.
Jose Luis Magana/AP Photo
Smoke billows from a Baltimore liquor store that was looted in a third day of violence in the city, April 8, 1968.
Baltimore News-American/AP Photo
Baltimore Police form a perimeter around a CVS pharmacy that was looted and burned near the corner of Pennsylvania and North avenues in Baltimore during violent protests, April 27, 2015, following the funeral of Freddie Gray, who died after apparently being injured in police custody.
Chip Somodevilla/Getty Images
A man carts off a television set during looting incidents in Baltimore, April 7, 1968. Many businesses were broken into, looted and burned during the riots.
A looted wig shop is seen damaged in Baltimore, April 28, 2015.
National Guardsmen seal off a business-residential section of Baltimore and prepare to use tear gas against looters on April 8, 1968.
Baltimore police officers push back a protester on Reisterstown Road near Mowdamin Mall on April 27, 2015 in Baltimore.
Drew Angerer/Getty Images
Pictured is one of four men arrested by police in downtown Baltimore on April 8, 1968. William A. Smith, an Associated Press photographer, said he saw police confiscate whiskey bottles filled with gasoline.
Demonstrators jump on a damaged police vehicle during clashes in Baltimore, April 27, 2015. Several Baltimore police officers were injured on Monday in violent clashes with young people after the funeral of Freddie Gray, who died after apparently being injured in police custody.