A report by the US Secret Service says one-third of the attackers who terrorized schools, houses of worship or businesses nationwide last year had a history of serious domestic violence.
Two-thirds had mental health issues, and nearly all of them had made threatening or concerning communications that worried others before they carried out the attack.
The Secret Service's National Threat Assessment Center studied 27 incidents where a total of 91 people were killed and 107 more injured in public spaces last year.
That includes the shooting at Marjory Stoneman Douglas High School in Parkland, Florida, were 17 people were killed and 17 others injured, and the fatal attack at the Tree of Life Synagogue in Pittsburgh.