This story is true.
On May 15, 1995, James Davis, age 56, killed 3 people and hurt two others on May 15, 1995, at the Union Butterfield plant in
Asheville, North Carolina.
According to a lawsuit filed against the company, the employer knew of James Davis's violent tendencies but failed to lock the doors, add extra security, or monitor the parking lot.
A USA Today study of 224 cases of workplace violence showed that, In nearly eight of 10 cases, killers left behind clear warning signs -- sometimes showing guns to co-workers, threatening their bosses or talking about attacking.
(Data taken from http://www.workplaceviolence911.com/docs/20041012.htm)