A week after UnitedHealthcare CEO Brian Thompson was shot and killed in New York, the health insurer's parent company is praising him as "one of the good guys" and seeking to both console employees and reassure them that their work makes a difference.

In a message to the company's nearly 400,000 employees, Andrew Witty, the CEO of UnitedHealth Group -- UnitedHealthcare's parent company -- confirmed Thompson was laid to rest on Monday and that colleagues gathered in Minnesota on Tuesday for a memorial.

"I know this has been an extraordinarily difficult week," Witty said in the letter, obtained by ABC News. "Our company remains in a state of mourning."

Referring to Thompson, 50, who had led the world's largest health insurer since 2021, Witty said: "It was a life lived to the absolute fullest. And a life that helped make a profoundly positive impact on the lives of so many people. People he never saw. People he never met. People who never knew him. But people Brian cared so deeply about."

He added: "Brian was one of the good guys. He was certainly one of the smartest guys. I think he was one of the best guys. I'm going to miss him. And I am incredibly proud to call him my friend."

Thompson's killing thrust the nation's health care industry into the spotlight.

When suspect Luigi Mangione was arrested in Altoona, Pennsylvania, earlier this week, investigators discovered he had writings with him that criticized health care companies.

A bulletin from the New York Police Department warned of heightened risks to health care executives in the wake of the shooting, citing social media posts that expressed frustration with the health insurance industry and celebrated Thompson's death.

Witty's letter to employees said the best way to remember Thompson "is to carry on his legacy — continuing to do right by the people who've entrusted us with their care and those who are counting on us to take care of their loved ones."

The letter added: "We owe it to Brian to make good on our promise to make health care work better for everybody, in every way."

Witty's letter also shared messages of support from people who shared their sympathies and described how UnitedHealthcare had helped them. He said the company has received thousands of phone calls, text messages, comments and emails offering condolences and gratitude.

"I am super proud to be a part of an organization that does so much good for so many and to have the opportunity to work alongside some of the most compassionate, most dedicated and truly brilliant people in health care," Witty said in the letter. "I hope you feel that, too."