The heavily armed woman who attacked a private Nashville school on Monday, killing three students and three staff members before being shot dead by police is a former student, authorities say.

Five of the victims were pronounced dead at nearby Monroe Carell Jr. Children’s Hospital at Vanderbilt; the sixth was pronounced dead at the scene, according to authorities.

“It could have been far, far worse,” said Metro Nashville Police Department Chief John Drake. “We have an ongoing investigation as it pertains to her at this time.”

Police say the 28-year-old woman who opened fire at Nashville’s Covenant School was a former student armed with two “assault-type” rifles and a handgun. The Covenant School is a small, private Christian school.

Police said responding officers found and killed the woman on the school’s second floor as she continued firing. She apparently entered the school through a side door, police said.

The shooter parked her car nearby, which helped police identify her. Drake said she lived in the Nashville area.

The school victims have been identified as:

9-year-old Evelyn Dieckhaus

9-year-old Hally Scruggs

9-year-old William Kinney

61-year-old Cynthia Peak

60-year-old Katherine Koonece

61-year-old Mike Hill

Shooter, who was killed by police has been identified as 28 year old Audrey Hale

According to Statista, only three mass shootings since 1982 were committed by women, compared to 135 by men. Since 2013, the source defines a mass shooting as any single attack in a public place with three or more fatalities, in line with the definition by the FBI. Before 2013, a mass shooting was defined as any single attack in a public place with four or more fatalities.

According to The Violence Project, this is the first time since at least 1966 that a woman committed a solo mass school shooting at a K-12 institution.