Officials said they could identify no definitive links between the disturbances — a bombing that hurt 29 in Chelsea, an explosion along the route of a scheduled race in Seaside Park, N.J., and a stabbing that wounded nine in a St. Cloud, Minn., mall.
Police say the suspect made references to Allah and asked one of the victims if they were Muslim. His motive remains unknown.
After the attack at the Crossroads Center mall, witnesses say victims warned other to run away.
The blast occurred about 9:35 a.m. Saturday along the route of the Seaside Semper Five Marine Corps Charity 5K.
Authorities say none of the injuries are believed to be life-threatening.
Police recovered a rambling letter from the gunman that expressed hatred of police and probation officers.
The officer was indicted on a charge of firing into a car filled with teenagers, injuring two of them.
Police say they were responding to a reported armed robbery when they encountered the boy.
The man was taken to a hospital after the encounter, according to reports.