Three people, including a shooter, were killed by gunfire Saturday at a shopping mall in Columbia, Maryland, dpa reported.
Police were confident it was a single shooter, said Bill McMahon, chief of Howard County police, in broadcast remarks.
Many in the weekend shopping crowd took cover and found hiding places, as the general public has been instructed to do. Police were scouring the mall to find anyone still sheltering, police said.
Columbia is 60 kilometres north of Washington, DC.