Gahler said Thursday's gun violence began outside the warehouse and then moved inside, but investigators were still piecing together the precise sequence of events.
A 26-year-old woman open fired in a warehouse in the U.S. state of Maryland, killing three people and wounding several others before taking her own life, according to authorities and a witness account.
Deputies were dispatched at 9:09 a.m. ET, the sheriff's office tweeted.
Three others who were also shot are expected to survive, he said. Both the shooters in the latter two incidents were killed by police.More news: "Small Men Who Lack Vision": Imran Khan Slams India Over Cancelled Talks
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"The First Lady and I are grieving for the loss of life in today's shooting in Harford County and praying that those who were injured fully recover". No law enforcement officials fired any shots, Gahler said. "It went to voicemail because they keep their phones in lockers", said Kelly Rodriguez, 40.
The shooting is believed to have taken place at or near a drugstore distribution center named Rite Aid.
The attack comes nearly three months after an attacker killed five people in a newspaper office in Annapolis, Maryland. Authorities accused Jarrod W Ramos of attacking The Capital Gazette because of a longstanding grudge against the paper.
The suspect -a 26-year-old identified as Snochia Moseley - died after shooting herself in the head, Harford County Sheriff Jeff Gahler told reporters. She described it as a support facility adjacent to a larger building.
The incident is no longer an active shooter situation as of 11:30 a.m. local time.
FBI Baltimore said it was responding to the scene, and a spokesperson told Fox News one of the bureau's crisis specialist teams was en route.
The situation was "still fluid", the Harford County sheriff's office said on Twitter.