There were 757 instances of deadly violence in the workplace in 2018, according to the Bureau of Labor Statistics, from office shootings to stabbings to suicide. Many nonfatal incidents go unreported.

If you believe a co-worker poses an imminent danger of physical violence, your best option is to call 911, said Matthew Doherty, who formerly ran the Secret Service’s National Threat Assessment Center and now teaches about early warning signs.

Often, the threat of violence in the workplace is not from co-workers, but from domestic partners or other family members. Forty percent of women who died in workplace homicides in 2016 were killed by a domestic partner or relative who showed up to her place of employment.

But before a situation escalates to that point, there are usually warning signs and opportunities for intervention that don’t involve the police.

Frequent, intense changes in behavior could be cause for concern. Think not just one irritable Monday, but a pattern of aggressive outbursts, for example.

Beyond direct threats of bodily harm, “any type of disruptive behavior that causes fear” or threatens the work environment or safety of workers are reasons to be on alert, Doherty said.

The majority of people who commit public acts of violence say or do something that might worry co-workers, friends or family members, such as taking an interest in previous incidents of workplace violence, making racist and misogynistic comments, or expressing a desire to purchase a gun or commit violence, according to a 2018 report from the Secret Service’s NTAC.

Doherty has also dealt with cases of laid-off employees who return to the job site and make overly aggressive, inappropriate statements like, “Give me my job back or else,” or, “I’m holding you responsible and you’re going to pay for this.”

Because domestic violence can lead to workplace violence, managers should be trained to notice signs of abuse among their direct reports, such as uncharacteristic lateness or absence; new moodiness, depression or distraction; injuries, especially if the person is trying to conceal them with clothing or an unusual amount of makeup; or displacement from their home.

Your primary responsibility is to share or report your concerns, not investigate them. Asking your co-worker about the change in their behavior should be done only if you are familiar and comfortable with them, and you should first consult an in-house security expert if your workplace has one.

If you do talk to the co-worker, try to withhold judgment. Ask how they are doing, and neutrally state what you have observed about changes in their behavior. Or, if they have said something concerning, you can ask for clarification, like, “What exactly did you mean by that statement?”

Giving the co-worker a chance to share their side of the story may diffuse hostility later on, threat assessment experts say.

You may still need to report them, and many workplaces have different channels to do so, including your supervisor, an anonymous ethics or compliance hotline, human resources or corporate security.

Most corporate policies include a zero-tolerance rule for workplace violence, but a good violence-prevention program should make it clear to all staff that the goal of reporting is not to punish someone, but to get them help. This may come in the form of employee assistance programs, which can address common stressors inside and outside the workplace. For everyone’s long-term safety, employees should advocate for better access to and less stigma around using EAPs.

For victims of domestic abuse, company management can help by ensuring the place of employment is listed in a protective order. For people suffering job loss, help could come in the form of extending benefits and severance to soften the blow of losing work.

If your company lacks resources to deal with warning signs, you can help organize across departments and coordinate with key people, said Marisa Randazzo, CEO of Sigma Threat Management Associates. She suggests simultaneously emailing HR, corporate security and legal counsel to alert them to a situation. “I have a situation I don’t know how to manage here,” she suggested as a potential template. “I’m scared about the potential for violence. Let’s all of us talk together and see what’s going on.” That can also help the workplace see when it needs to bring in an outside expert in threat assessment.