SACRAMENTO, Calif.—The nation's largest teachers' pension fund announced Tuesday that it will review its holdings after being criticized for having an investment in the manufacturer of an assault rifle used in last week's Connecticut school massacre.

The California State Teachers' Retirement System, which manages $155 billion in assets, is making sure its investments comply with the fund's own social and ethical standards. Spokesman Michael Sicilia said it will take days for the fund to compile a list of firearm holdings.

The fund invested $600 million in the private equity firm Cerberus Capital Management, which owns gun maker Freedom Group International. Cerberus announced Tuesday it will sell its holdings in the manufacturer of the military-style rifle used to kill 20 schoolchildren and six adults at Sandy Hook Elementary School in Newtown, Conn.

"These are tragic and devastating acts that took place at Sandy Hook and they have prompted many in this country to call for change and we're determining what we can do differently to help ensure that this unthinkable act never happens again," Sicilia said.

State Treasurer Bill Lockyer has asked CalSTRS and the state employees' pension fund to reconsider any investments in firearm manufacturers. Lockyer, a Democrat, is a member of the pension board and has a say in the fund's investment strategy.

According to CalSTRS, the fund invested $100 million in Cerberus in 2003 and another $500 million in 2007. Cerberus cobbled Freedom Group together by buying Bushmaster, Remington, and other well-known gun brands starting in 2006. As a result, CalSTRS says it owns 2.4 percent of Freedom Group.

Since the 1980s, the retirement system has included political and social risks in its investment strategy. That includes risks associated with products that pose significant threats to human well-being. However, the policy was not expanded to include the fund's private equity investments until 2008, after CalSTRS invested in Cerberus.

Sicilia said the fund is now reviewing for other firearm holdings prior to 2008.

"We are making sure that we're going to through all of our investments to make sure that those criteria are taking into consideration," he said.