LAWRENCE, Mass. (AP) — Federal prosecutors are 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 reportto 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.

Lelling's office declined to comment. A NiSource spokesman said the company is cooperating with all investigations and inquiries related to the incident.