Unfortunately, incidents of workplace violence are increasingly common.  One major risk for employers associated with workplace violence is the potential for a negligent retention claim.
Under Minnesota law, liability for negligent retention is “predicated on the negligence of an employer in placing a person with known propensities, or propensities which should have been discovered by reasonable investigation, in an employment position in which, because of the circumstances of the employment, it should have been foreseeable that the hired individual posed a threat of injury to others.”  See Bruchas v. Preventive Care, Inc., 553 N.W.2d 440 (Minn. Ct. App. 1996).
The case of Yunker v. Honeywell is instructive about what kind of evidence is necessary to establish that an employee’s violent actions were reasonably foreseeable by the employer.  496 N.W.2d 419 (Minn. Ct. App. 1993).  In Yunker, the court held that there was sufficient evidence that an employee’s murder of another employee while off-duty was reasonably foreseeable to the employer because:

While at the Golden Valley facility, Landin sexually harassed female employees and challenged a male coworker to fight.  After his transfer to St. Louis Park, Landin threatened to kill a coworker during an angry confrontation following a minor car accident.  In another employment incident, Landin was hostile and abusive toward a female coworker after problems developed in their friendship.  Landin’s specific focus on Nesser was demonstrated by several workplace outbursts occurring at the end of June, and on July 1 the words “one more day and you’re dead” were scratched on her locker door.

Landin’s troubled work history and the escalation of abusive behavior during the summer of 1988 relate directly to the foreseeability prong of duty.

Id., at 424.
Takeaways:  The Yunker case shows that an employee’s violent behaviors and threats towards other employees may be sufficient in certain circumstances to make violence towards co-workers reasonably foreseeable to an employer.  To avoid liability, employers who confront violent behaviors or threats by employees should be prepared to take action to prevent harm, if necessary.  What type of corrective actions may be necessary will likely depend on the circumstances of each case.  In some cases, discipline or termination of the employee may be sufficient.  In more severe cases, it may be necessary to call the police or take other security precautions.