Shootings on Friday at two Maryland shopping centers eight miles apart killed two people and injured two others, although it was unknown if the incidents were related, police said.
Police were also looking into whether Friday's incidents could be tied to another shooting a day earlier, in Beltsville, about 10 miles east of Silver Spring.
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Eulalio Tordil, 62, identified as a person of interest in the shootings, was arrested Friday afternoon. He is accused of shooting and killing his estranged wife and injuring a bystander in a high school parking lot, authorities said.
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Tordil is a police officer with the Federal Protective Service, a U.S. Department Homeland Security agency responsible for security at federal buildings and some foreign embassies in the Washington area.
He was put on administrative duties in March after a protective order was issued against him, Homeland officials told NBC News. He was later placed on administrative leave, required to surrender his government-issued weapons, badge, and credentials.
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He had threatened to commit "suicide by cop," police said.
The violence started at the Westfield Montgomery Mall in Bethesda, where two males and one female were injured by gunshots following a "confrontation" in the parking lot, Montgomery County police said. One male later died at the hospital, police said. Another was in critical condition, and the female had non-life-threatening injuries, reported NBC News.
Two of the wounded were bystanders who came to the aid of the first victim, said Assistant Chief Darryl McSwain of Montgomery County police.
About 20 minutes after that shooting, police responded to more gunfire about 8 miles away at a Giant Food supermarket at the Aspen Hill Shopping Center in Silver Spring, where a woman was fatally struck.
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"We have no reason to believe the victims knew the suspect," McSwain said, to various media. "But we are certainly looking at all angles.
Authorities, meanwhile, locked down nearby schools and recreational facilities.