The Suffolk County Grand Jury yesterday indicted a former employee of the Massachusetts Society for the Prevention of Cruelty to Animals for allegedly setting a fire in the agency’s headquarters, which housed animals and veterinarians at the time, Suffolk County District Attorney Daniel F. Conley announced.

WILLIAM FITZGERALD (D.O.B. 4/19/58) of Plymouth is expected to be arraigned tomorrow in Suffolk Superior Court on charges of arson of a dwelling, willful and wanton destruction of property, and injury to a firefighter.

The indictments allege that FitzGerald started a fire on the fourth floor of 350 South Huntington Ave. late on Feb. 19. FitzGerald is a former MSPCA manager of building and grounds; he has since been terminated from that position.

The MSPCA administration has “cooperated with our investigation since day one,” Conley said.

At the time of the conflagration, the Jamaica Plain building contained most of the agency’s offices, sheltered more than 200 animals, and served as a residence for a number of resident veterinarian students. The building was evacuated before any animals or staff members were injured, but the fire, smoke, and water caused about $400,000 in damages and destroyed files that dated back to the 1930s.

“We’re all extremely lucky that no lives were lost,” Conley said. “There was a very real potential for injuries and much, much worse.”

Yesterday’s indictments come as the result of a three-month investigation by Boston Police detectives, Boston Fire Department investigators, and Suffolk County prosecutors. The grand jury investigation was led by Assistant District Attorney Julie Higgins.

FitzGerald is represented by attorney Kevin Reddington. Proceedings are expected at or around 9:30 in the Magistrate’s Session of Suffolk Superior Court, located on the seventh floor of Three Pemberton Square.