Ann Rule, a best-selling true-crime writer, worked side by side with Ted Bundy, one of the nation's most notorious serial killers, at a Seattle suicide hot line in the early 1970s. Yet, Bundy's on-the-job behavior never raised the hairs on the back of her neck.

Rule, a former policewoman and social worker, said it might have been a different story if she had worked with Gary Ridgway, another of the nation's worst serial killers. At work, Ridgway would make degrading remarks about women and invade their personal space, said Rule, who wrote a book about the Washington state serial killer, "Green River, Running Red."

"I do think in an office situation if people are concerned about someone, they should go to their bosses," Rule said.

Yet, most employees and managers don't raise alarms when a co-worker is giving off signs that they might be capable of violence, human resource and workplace security experts said. After a violent workplace incident, co-workers and managers can have tremendous guilt if they didn't speak up, workplace experts said.

Security experts said that in recent years, awareness has grown about the potential for people to "go postal," a term coined after postman Patrick Sherrill killed 14 co-workers at the post office in Edmond, Okla., in 1986.

"People don't just snap. They tend to plan out their activity," said Philip S. Deming, a Pennsylvania consultant specializing in human resource and security risk management.

Vicki Myoda, owner of Freelance HR LLC in Wilmington, was working in human resources at a Delaware company when a manager robbed a bank.

"When I was talking to the people who worked for him, afterward they all said, 'Yeah, we knew something was up.' Every person knew he was acting oddly," Myoda said.

The workers, who had discussed the man's behavior among themselves, said they kept mum because they felt the company couldn't — or wouldn't — do anything about it, she said.

Feeling safe at work ranks as one of the top factors in job satisfaction, according to a 2006 survey by the Society for Human Resource Management.

As a result, most large companies and state and local governments now have methods to try to identify workers, potential hires, customers or visitors with a history of violence, according to the U.S. Bureau of Labor Statistics. Eighty-two percent of large employers have a written workplace violence prevention program.

Perhaps because of an increased emphasis on prevention, workplace homicides have dropped nearly in half from 1992 to 2005, according to the labor statistics bureau.

But recent shootings and attacks, including two apparent employee-on-employee killings, emphasize the importance of employees speaking up, said Timothy Dimoff, an Ohio consultant who specializes in workplace risk issues.

In one of the shootings, a contractor at NASA's Johnson Space Center in Houston, who reportedly thought he was going to be fired, shot and killed his supervisor.

In another incident, a former employee of a Target department store in Kansas City, Mo., shot and killed two people in a mall parking lot after he was turned down for a private security license.

Those shootings followed the country's worst mass killing, at Virginia Tech in Blacksburg, Va., where 32 people were murdered in April.

Not all violent acts are killings. The Bureau of Labor Statistics defines a violent act at work as a physical assault, threat of assault, harassment, intimidation or bullying.

Five percent of all of the country's work establishments, including state and local governments, had an incidence of workplace violence in the previous year, according to a survey by the labor statistics bureau.

Those figures include violence by customers, clients, patients or students, or people who had a personal relationship with an employee.

But co-workers committed most violent acts at larger employment sites in 2005.