Once upon a time, employees who were dissatisfied with how management treated them might respond by organizing, filing a grievance or suing. If they were really frustrated, they might refuse to sign the warning notice or performance appraisal form that was presented to them in protest.

Nowadays it is not uncommon for disgruntled employees to push the boundaries of behavior much further, even to the point of killing supervisors or managers.

Six recent episodes

From June 2015 through September 2016 the following tragedies occurred:

• Jason Yanko, 40, an operations manager in Texas was shot several times by an employee he was in the process of firing. Investigators identified 25 spent shells at the scene. Yanko's body was found clutching the termination paperwork in his hands. The employee was later sentenced to life imprisonment for Yanko's murder.

• Ward R. Edwards, 49, a manager in Indiana, was killed in a conference room by an engineer who reported to him. After shooting Edwards, the man took his own life. As is usually the scenario with deadly violence, the incident threw the workplace, with a reported 1,100 workers, into chaos.

• Andrew Little, 55, a supervisor at a landscaping company in Florida, was shot to death. The employee charged with Little's murder reportedly felt he was being disrespected, was not being compensated fairly, and had prior run-ins with Little and others, but mainly with Little. According to the police report, the suspect ran to his vehicle after the shooting and retrieved a baseball bat before being arrested. While in jail awaiting trial on Little's murder, he was charged with a second felony.

• Air Force Lt. Col. William Schroeder, 39, commander of the 342nd Training Squadron in Texas, was murdered by a technical sergeant who was facing discipline. As he struggled to gain control over the shooter who was brandishing a glock, Schroeder valiantly warned others in the area to run. Bullets struck Schroeder in the arm and the head. The shooter then committed suicide.

• Mike Dawid, 35, a Texas manager was killed by a former employee who returned to the workplace two weeks after his termination. Flying glass caused by shotgun blasts injured employees who were working in the area at the time of the shooting. The ex-employee then killed himself.

• Sandra Cooley, 68, and James Zotter, 44, supervisors at a factory in Tennessee, were killed by Ricky Swafford, 45, a long-term employee who they had been meeting with. Swafford became upset, left the meeting and returned to shoot them before killing himself. Zotter had just been promoted to supervisor a week before his murder.