The fatal shooting of an executive on the streets of New York City plunged his family members and colleagues into grief. For rank-and-file employees across the health insurance industry, the killing has left them with an additional emotion: fear, with many frightened for their own safety and feeling under attack for their work.

Health insurance companies have increased security measures since the killing of Brian Thompson, the CEO of UnitedHealthcare, and as an outpouring of online rage toward the industry has followed. Health care leaders have spoken with frustration about feeling vilified, and in the Minneapolis suburbs where United is headquartered, police officers stepped up protection of the company’s offices.

“Clearly the employees have been shaken,” said Brad Wiersum, the mayor of Minnetonka, Minnesota, who added that the city was working “just to provide that reassurance and that security, to let people know that we are going to do everything we can to keep them safe.”

One UnitedHealthcare worker who processes claims described being clear-eyed about the American health care system’s shortcomings, but also believes that she and her colleagues do their best to help patients within the limits of that system. Like most workers interviewed, she did not want to be named because, given the reaction after Thompson’s killing, she feared for her own safety.

The reaction by some others to the killing, the employee said, had been startling and horrifying. The worker, who has been at the company for many years, described being told in recent days by an acquaintance that as an employee of UnitedHealthcare she was responsible for millions of people being denied lifesaving care, and that if she had any ethics, she would see the killing as the impetus to quit her job.

One former employee of UnitedHealthcare described seeing glib, distasteful messages about Thompson’s death even in a Facebook group composed largely of people who work in the industry. Another former employee described being stunned by the torrent of hate directed at her industry, and a pervasive feeling of fear that had prompted changes to meeting schedules at work. Like others, those workers spoke on the condition of anonymity because of concerns about their safety.

All of the tumult was leading some to raise questions about the industry’s direction, even as many executives complained that they thought portrayals of their companies were unfair and rooted in incomplete or inaccurate information.

“It’s a moment of reckoning for the health care industry, more broadly,” said Dr. Sachin H. Jain, CEO of SCAN Group and SCAN Health Plan. “We’ve unmasked a sentiment that things need to change.”

But just what, if anything, might change remained unclear as much of the sector remained in a stunned state. Social media posts grieving Thompson brought a deluge of angry comments about claim denials and problems accessing care.

Other health companies boosted protection for their executives, and one, Centene, announced that it was moving an investors’ event online in light of Thompson’s death. Andrew Witty, the leader of UnitedHealth Group, the parent company of UnitedHealthcare, sought to reassure worried employees in a video message that was obtained by CNN and other news outlets.

The killing, Witty said in the video, “might make you feel nervous, it might make you feel anxious, and certainly may be very disturbing.”

Witty encouraged workers to ask for help if they needed it as they grieved Thompson, a husband and father who was mourned at a private funeral this week.

UnitedHealthcare officials said the company began providing support services for employees immediately after the shooting, including individual and group counseling, as well as flexible work options. The company also held an internal ceremony to mourn Thompson that was attended by hundreds, and reported receiving many phone calls of support at its call centers.

Still, tensions remain high. Minnetonka police records show that officers had taken calls at United in recent days, including one in which they asked a journalist to leave the property and another in which they investigated “vague threats in the past” by a former employee.

In interviews, insurance executives, many of whom spoke on the condition of anonymity because of concerns over their safety, described people in their circles feeling newly rattled.

“I think people are traumatized, absolutely traumatized, and probably also scared,” a former executive at UnitedHealthcare’s parent company said. “This is not on anybody’s map of possibilities,” the executive said of the slaying of Thompson.

Several executives described feeling that simply by playing their role in the system, insurers had unjustly been cast as villains. The industry had not always done a good job of explaining itself to customers, some acknowledged, even as they expressed frustration with characterizations they saw as unfairly negative. Many expressed a belief that, despite imperfections, their companies play an important role in keeping costs down and helping patients access appropriate care.

As health care costs have climbed, Americans have become increasingly frustrated with having to pay more for insurance, only to find when they need care that they still face large medical bills because their plan often does not cover the full expense. Other patients have had to battle the insurers over getting treatment as the companies have become increasingly aggressive about requiring authorization and denying care they consider unnecessary.

The arrest Monday of a suspect in Thompson’s killing seemed to do little to quiet the fear in the industry, especially as some online commenters treated the accused assassin as a folk hero. The suspect, Luigi Mangione, 26, who was recognized at a McDonald’s in Pennsylvania from images circulated by the police, was charged late Monday with second-degree murder, forgery and three gun charges.

Mark Bertolini, a former CEO of Aetna who is now CEO of Oscar Health, a small health insurance company, said he saw the shooting reflecting a national mood in which “people are just frustrated and angry at everything.”

But as his industry seeks to move forward, he said, its leaders needed to do so recognizing the pent-up frustration Americans have with the health care sector.

“We can’t ignore the anger,” Bertolini said. “We have to understand it within its context.”

In a message sent to employees Wednesday evening, Witty stressed the positive impact the company has on people’s lives and getting the care they need. “Never forget: What you do matters. It really, really matters. There is no higher calling than helping people. Nothing more vital to the human condition than health care. And while these days have been dark, our patients, members, customers are sending us light.”