When a brewery employee gunned down five co-workers at Milwaukee's Molson Coors campus, then killed himself, it was the first mass shooting at a workplace involving a current or former employee in 2020.
The incident marked the 13th mass workplace shooting by a current or former employee since 2006, according to a database of mass killings maintained through a partnership between USA TODAY, The Associated Press and Northeastern University.
"Mass shootings are a rare event and at a workplace even rarer," said James Alan Fox, a professor of criminology at Northeastern who tracks the data.
In 2020, there have been more than 2,300 gun violence deaths, which doesn't include more than 3,800 by suicide, in the USA, according to the Gun Violence Archive.
Since 2006, 90 people have died in the 13 mass workplace shootings, according to the USA TODAY, AP and Northeastern database.
Milwaukee shooting is most recent of rare phenomenon
That's 5% of the 1,800 victims of the 331 mass shootings since 2006. About 40,000 Americans die from firearm-related injuries each year, according to the Centers for Disease Control and Prevention.
"It's horrific when it happens," Fox said. "But what we do know about mass shootings is that fear is out of proportion with actual risk."
The database includes mass killings during which four or more victims are killed, not including the assailant.
Last year saw more mass killings than any other year dating back to at least the 1970s, according to the database. There were 41 mass killings, of which 33 were mass shootings.
The Molson Coors shooting comes less than a year since a former employee at a municipal building in Virginia Beach, Virginia, opened fire, killing 12 people. The gunman was killed by police in May 2019.
In Aurora, Ilinois, an employee at a manufacturing plant killed five co-workers in February 2019. After a 90-minute shootout, officers killed the gunman.
Workplace shootings follow similar pattern
Many cases involving a current or former employee follow a similar pattern, Fox said.
Often, gunmen are longtime employees who feel wronged by the company or believe their work is not appreciated.
The employees may be older and recently fired. "Someone who is in their 50s, there may not be another opportunity," Fox said.
Some cases involved disputes between employees, Fox said.
At Molson Coors, the alleged gunman had been involved in a long-running dispute with a co-worker that boiled over before he started shooting, according to a law enforcement source who spoke to the Milwaukee Journal Sentinel and brewery sources.
The shooter worked as an electrician for more than 20 years, about 17 of them at Molson Coors, according to multiple sources and online employment records.
A co-worker who asked not to be identified for fear of being disciplined said the alleged assailant believed he was discriminated against because he was African American, and he frequently argued with at least one of the victims, a fellow electrician.
Killings by disgruntled customers and clients increase
Since 2006, there have 25 mass shootings at commercial locations with 161 victims, including incidents in which the shooter was not a former or current employee, according to the USA TODAY, AP and Northeastern database.
Fox said the number of workplace homicides, not just mass killings, involving current or former employees stayed roughly constant from 1997 to 2015.
Since 2011, the number of firearm-related workplace homicides has fluctuated from 350 to 400, according to the Bureau of Labor Statistics Census of Fatal Occupational Injuries. In 2018, 351 people were killed in a workplace homicide involving a firearm.
Cases of disgruntled customers or clients killing one or more people at commercial locations have increased, Fox said. In 1997, there were 20 such cases,he said. That grew to 70 by 2009 and leveled off to 50 by 2015.
Though the risk of disgruntled employees opening fire is low, the impact on the workplace is often much greater, Fox said.
A business may change security protocols after an incident or nearby workplaces may hold training, he said.
Contributing: Mitchell Thorson, George Petras and Grace Hauck, USA TODAY; Gina Barton, Annysa Johnson, Rick Barrett and John Diedrich, Milwaukee Journal Sentinel