Marchers protest police violence in Baltimore, New York

New York Police Department officers detain a protester during a march through the Manhattan borough of New York City calling for social, economic, and racial justice April 29, 2015. [Photo/Agencies]

With police and National Guard troops patrolling Baltimore's streets on Wednesday, schools reopened and business resumed.

Baltimore's Major League Baseball team, the Orioles, played the Chicago White Sox in an empty stadium, a sign of the tenuous security situation.

Police have arrested close to 270 people since Monday, 18 of them on Wednesday. Police Commissioner Anthony Batts said more than 100 people had been released without being charged, because officials could not keep up with the paperwork, but he said charges would be brought later.

Numerous stores were looted on Monday and 20 officers were hurt by rioters throwing stones and bricks.

The violence in Baltimore prompted national figures - from the new U.S. Attorney General Loretta Lynch to Democratic presidential hopeful Hillary Clinton - to weigh in and vow to work on improving law enforcement and criminal justice in minority communities nationwide.

Lynch, sworn in as attorney general on Monday, called Baltimore's riots "senseless acts of violence" that are counterproductive to the ultimate goal of "developing a respectful conversation within the Baltimore community and across the nation about the way our law enforcement officers interact" with residents.

The Baltimore neighborhood that saw the worst of the violence was already filled with many burned-out buildings and vacant lots that had not been rebuilt since the 1968 riots that followed the assassination of civil rights leader Martin Luther King Jr.