LAWRENCE, Mass. (AP) — There's no evidence to suggest the gas explosions that rocked communities north of Boston were intentional, a federal investigator said Saturday.

As federal officials opened their investigation into Thursday's disaster, National Transportation Safety Board Chairman Robert Sumwalt said that there doesn't appear to be "anything nefarious, anything suspicious, anything intentional."

He said investigators will be working to develop a timeline going back at least three weeks, including reviewing any reports of gas odors reported by residents in the impacted communities of Law...