CONCORD, N.H. — An independent investigation into sexual misconduct at a New Hampshire prep school has expanded to include 18 former faculty and staff members dating back decades.

St. Paul’s School released a report in May detailing allegations against a dozen men and one woman who worked at the school between 1947 and 1999. An addendum released Wednesday includes five staffers never identified before and outlines abuse that occurred up to 2009.

St. Paul’s requested the investigation last year following reports about Howard White, who was fired from St. George’s School in Rhode Island for sexual misconduct in 1974 and had previously worked at St. Paul’s.

Rector Michael Hirschfeld said in a letter to parents the accounts of abuse were “upsetting” as was the fact that the school had failed to protect students.