Jason Rodriguez, a former employee of Reynolds, Smith & Hills in Orlando, Fla., is accused of returning to his former workplace and shooting employees. And Army Maj. Nidal Malik Hasan is accused in a rampage at Fort Hood that left 13 dead. We look at the reasons behind workplace violence and other cases.

Economic woes: Unemployment and layoffs are reasons why many workers fear violence. Killings at work are unusual (how rare are they?).

Warning signs: Here are some suggestions for spotting potential problems and how businesses can prevent them. What are other warning signs?

Don't say it: A rash of postal service rampages in the late '80s and early '90s led to this phrase. This man's 1986 rampage was the worst.

Deadly co-workers: A woman's mass murder of co-workers was perhaps the deadliest workplace shooting this decade. Here are the details.

Racial tensions were behind Doug Williams' slaughter of six co-workers at a Lockheed Martin plant in 2003.

The recent slaying of graduate student Annie Le stunned the Yale University community. Her alleged killer, Raymond Clark, didn't fit the profile of a dangerous employee.

The most violent job: These caregivers suffer the most assaults and attacks. (Find out about other violent jobs.)