Police say the gunwoman suspected of shooting and killed three people and injured several others before killing herself at a Rite Aid distribution centre in the US was diagnosed with mental issues earlier this year.
Harford County Sheriff Jeffrey Gahler said investigators searched 26-year-old Snochia Mosley's residence and found no evidence of a motive, but did find Mosely was diagnosed with a mental illness.
"Overnight the detectives interviewed family members and friends and executed a search warrant at the residence of the shooter looking for some motive or some cause.
"While no evidence directly related to the shooting was recovered, evidence that the shooter was suffering with a mental illness was identified. Friends and family members relayed to detectives that over the last two weeks she had become increasingly agitated and that they were concerned for her wellbeing."
The gun she used was legally purchased.
Investigators say Mosley showed up for work around 9am and began shooting people both inside and outside the facility. She then turned the gun on herself.
Mr Gahler identified the three people killed as a 45-year-old man, Sunday Aguda, of Baltimore County, and two women, 41-year-old Brindra Giri, of Baltimore County and 41-year-old Hayleen Reyes from Baltimore City.
Mr Gahler said the three injured and being treated are 19-year-old Hassan Mitchell of Harford County, 45-year-old Welfredo Villegas of Montgomery County and 45-year-old Acharya Purna from New York.
Only 4 percent of US mass shooters are women, an expert told the New York Post.
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