The leader of UnitedHealth Group conceded that the patchwork U.S. health system “does not work as well as it should” but said Friday that the insurance executive gunned down on a Manhattan sidewalk cared about customers and was working to make it better.

UnitedHealthcare CEO Brian Thompson, who was killed last week, was described as kind and brilliant by UnitedHealth Group CEO Andrew Witty in a guest essay published in The New York Times.

The killing has been viewed as a violent expression of widespread anger at the insurance industry. Witty said people in the company were struggling to make sense of the killing, as well as the vitriol and threats directed at colleagues.

Police have said that the man charged with killing Thompson, Luigi Mangione, was found with a three-page letter in which he lamented the high cost of health care in the U.S. and singled out UnitedHealthcare for its profits and size. The company, a division of UnitedHealth Group, is the largest U.S. health insurer. Mangione is currently being held in Pennsylvania and intends to plead not guilty to a murder charge in New York, his lawyer has said.

Witty said he understood people’s frustration but described Thompson as part of the solution.

Thompson never forgot growing up in his family’s farmhouse in Iowa and focused on improving the experiences of consumers.

“His dad spent more than 40 years unloading trucks at grain elevators. B.T., as we knew him, worked farm jobs as a kid and fished at a gravel pit with his brother. He never forgot where he came from, because it was the needs of people who live in places like Jewell, Iowa, that he considered first in finding ways to improve care,” Witty wrote.

Witty said his company shares some responsibility for lack of understanding of coverage decisions.

“We know the health system does not…