The shooter who opened fire on a grade school in Nashville planned the attack for several months, investigators said Monday.
Audrey Hale, 28, wrote those plans in journals kept at home and had "considered the actions of other mass murderers," the Nashville Metropolitan Police Department said in a brief update.
Hale acted alone, and police said a motive for the shooting is still under investigation.
Hale was fatally shot by police after killing three 9-year-olds and three adult staff members at the Covenant School. Friends and law enforcement said Hale was transgender, and according to a LinkedIn profile, used he/him pronouns. A friend told ABC News that Hale recently transitioned and was going by Aiden.
Police have said that the shooter previously attended the private Christian school, which teaches preschool through sixth grade. In a car that the shooter drove to the school, police found writings that detailed plans "to commit mass murder." More of such writings were later found in Hale's bedroom, investigators said.
The journals are being reviewed by the police and the FBI.
Hale stormed the school building on the morning of the shooting armed with three firearms, which were purchased legally, police chief John Drake said.
According to police, Hale was seeing a doctor for an emotional disorder at the time but was not on law enforcement's radar.
Drake previously said that the shooter wrote a manifesto containing a map of the Covenant School, a drawing of how to enter the campus, and "the assaults that would take place." The manifesto also included the names of several other locations, but Drake declined to say if those places were targets as well.
The Nashville police's homicide unit is leading the investigation into the shooting. The Tennessee Bureau of Investigation is reviewing Hale's fatal shooting by police.