Report: Half of US mass attacks sparked by workplace disputes

Half of the violent mass attacks in the United States from 2016-2020 were sparked by personal, domestic or workplace disputes, and a gun was used for nearly three-quarters of the attacks, according to a Secret Service report released Wednesday.

The 70-page report — Mass Attacks in Public Spaces: 2016-2020— came days after a pair of mass shootings in California that took the lives of 18 people and as authorities searched for motives in the attacks linked to older men.

The sheriff's office said it believes the shootings at a California mushroom farm and at another nearby site on Monday were "workplace violence" but hasn't given a detailed motive.

Chunli Zhao, 66, the lone suspect in Monday's massacre at two mushroom farms in the seaside town of Half Moon Bay was charged Wednesday with seven counts of premeditated murder and a single count of attempted murder.

Los Angeles law enforcement authorities said investigators hadn't yet established why 72-year-old Huu Can Tran shot and killed 11 people and wounded nine Saturday night at a ballroom dance hall in Monterey Park, California. Tran later killed himself as police closed in on him.

The Secret Service report is an analysis of 173 mass attacks that occurred in 37 states and Washington DC, from major cities to small towns. It details attacks that hurt three or more people in public spaces, including churches and schools. It was done by the agency's National Threat Assessment Center (NTAC).

It aims to prevent violence by identifying warning signs.

Dr Lina Alathari, the chief of the center, said the trends could help community leaders know what red flags to spot before someone carries out a mass attack.

Although a personal grievance was the single most common motive for an attack, one-quarter of the attackers studied from 2016 to 2020 were motivated by conspiracy theories or hateful ideologies.

Hateful ideologies that motivated attackers included anti-government, antisemitic or misogynistic views. The authors of the report also found nearly one-third of all attackers had evidence of planning their attacks.

The typical attacker was a 34-year-old man motivated by personal grievances rather than ideology, the report says.

Alathari told NBC News the grievances could be "perceived wrongs, most often related to personal issues, maybe health or financial issues, workplace issues, as well as issues with family and romantic partners".

The Secret Service says in the five-year span of data the agency analyzed, 513 people were killed,and 1,234 people were injured.

Agencies contributed to this story.