A police officer stands outside High Point High School after a shooting incident in Beltway, Md., Thursday, May 5, 2016 (Photo: AP)
Shootings at two shopping centers in Washington suburbs killed one person and wounded three others on Friday, although it was known if the incidents were related and no suspects were in custody, police said.
Authorities locked down schools and recreational facilities as a precaution.
A confrontation led to the first shooting at Westfield Montgomery Mall in affluent Bethesda, Maryland, where two men and a woman were hit by gunfire and taken to a hospital, police said. They were in critical condition.
The incident was originally reported as an assault at about 11 a.m. (1500 GMT).
Two of the wounded were bystanders who came to the aid of the first victim, said Assistant Chief Darryl McSwain of Montgomery County police. There was no reason to believe they knew one another, he said.
No suspect was in custody but "we are looking at a person of interest," McSwain told a news conference in the pouring rain.
A second shooting about half an hour later killed a woman at the Aspen Hill Shopping Center in Silver Spring, some 8 miles (13 km) away, Montgomery County police said on Twitter.
Bethesda and Silver Spring are suburbs just north of Washington in Montgomery County, Maryland.
Investigators were unsure whether the two shootings were related, Montgomery County police spokesman Rick Goodale said.