David J. Holmgren, chief investment officer of Hartford HealthCare’s $4.3 billion in pension and endowment assets, and his entire investment staff were removed from their positions on Tuesday, said David M. Roth, former chairman of the health-care organization’s investment committee.

Mr. Roth, who resigned from his position as committee chairman on Thursday, said in a phone interview that company executives called a special meeting Tuesday of the investment committee to inform them that they had removed the investment staff and hired Morgan Stanley as outsourced chief investment officer.

Mr. Roth said he along with four other members of the seven-member investment committee have already resigned. In his own resignation letter, Mr. Roth cited a “total lack of transparency and deliberate bypassing of the investment committee and usurpation of its role.”

Mr. Roth said no member of the investment committee was aware of the impending change, nor that the company was considering moving to an OCIO model.

“They did not inform us, they did not ask for our help or whether making this change was a good idea or not,” Mr. Roth said.

A Hartford HealthCare spokeswoman emailed a statement saying that the company has reorganized its investment department and related functions.

“After careful review, and with the Board of Directors’ approval, we have made a decision to select a full-time investment firm to manage our portfolio,” the statement said. “Hartford HealthCare’s investment funds have performed well over many years.”

“The investment team’s acumen has earned national recognition from investment industry experts,” the statement said. “We are grateful for their many contributions of these colleagues, and will support them through this transition, either into new roles within the organization or to positions outside of Hartford HealthCare.”

The spokeswoman confirmed the hiring of Morgan Stanley as OCIO.

Mr. Holmgren; Jeffrey Flaks, president and CEO of Hartford HealthCare; and Richard Stys, senior vice president, finance and treasurer at Hartford HealthCare; could not be immediately reached for further information.