U.S. Investigations Services, which employs more than 300 in Grove City, has become the target of a $1 billion buyout, said an official close to the negotiations.

Buyout firm Welsh, Carson, Anderson & Stowe is negotiating to buy Annandale-based U.S. Investigations Services, which is one of the nation's largest employee-screening companies known for its unusual headquarters -- a former limestone mine 220 feet underground in Annandale, Butler County.

U.S. Investigations Services, which was part of the federal Office of Personnel Services until 1996.

The company has kept an extremely low profile since settling in the former Cooper Bessemer office about two years ago. The operation has shunned media inquiries and wouldn't permit presentations to its employees from local United Way representatives.

The official told The Associated Press on the condition of anonymity that the companies are scheduled to meet Friday to work out details of the deal, including share price, for employee-owned U.S. Investigations.

U.S. Investigations Services has about 3,600 employees worldwide and does background checks, drug- and alcohol-testing and provides security for the government and corporations. According to the company's Web site, it handles more than 1.2 million cases a year.

The tightly-held company doesn't report revenue or profit. But citing sources The Wall Street Journal reported the company this year will have about $500 million in revenue and about $100 million in earnings before interest depreciation and amortization.

A spokesman for New York-based Welsh, Carson, Anderson & Stowe declined comment.

Officials from U.S. Investigations Services did not return phone calls for comment to The Associated Press on Thursday. A spokeswoman for private-equity firm the Carlyle Group, which owns a 30 percent stake in the Pennsylvania company, said she could not immediately comment on the deal.