LAWRENCE, Mass. – Federal prosecutors have been conducting a criminal investigation into the natural gas explosions and fires that rocked three communities north of Boston in September.

NiSource, the parent company of Columbia Gas of Massachusetts, disclosed Thursday it is cooperating with a criminal investigation by U.S. Attorney for Massachusetts Andrew Lelling’s office. The Indiana-based utility made the disclosure in its quarterly financial disclosure report to the U.S. Securities and Exchange Commission.

NiSource says it was served initial grand jury subpoenas on Sept. 24, shortly after the Sept. 13 incident that killed one person, injured 25 others and damaged or destroyed more than 130 structures across Lawrence, North Andover and Andover. Thousands are still without natural gas service.

Lelling’s office declined to comment. Representatives of NiSource and Columbia Gas didn’t immediately comment.