"This is a good example of someone coming home, as we've asked, finding something wrong, and telling us right away", Moriarty said.
Michael Mansfield, the Andover fire chief, said: "I have never seen anything like this".
Investigators will also look at how local Columbia Gas officials responded to a "pressure increase" in the Lawrence area that was detected at the company's pipeline control center in Columbus, Ohio, prior to the explosions and fires.More news: Dutch intelligence claims foiling Russian plot to hack lab
"We're very interested to understand the operations of Columbia Gas", he said. "We will be looking at their record keeping, their procedural compliance, their procedures, their training, the oversight of their contractors", Sumwalt said Saturday.
Sumwalt said they will work to determine a cause for the incident and issue a preliminary report, but that a full detailed report on the exact cause may not be complete for up to two years. Leonel Rondon, 18, died after a chimney fell on his vehicle in Lawrence.
There is no evidence that anything nefarious contributed to the fires, Sumwalt said. He died at a hospital, authorities said.More news: Police investigating after needles found in Australian strawberries
In April this year, NiSource's Columbia Gas of MA filed a petition with the state's Department of Public Utilities to increase annual revenues in order to help the company replace aging infrastructure.
"We want to wholeheartedly thank the members of our police and fire departments who have worked nonstop and our utility companies, which are from all over the country, who are making these impacted homes safe".
"It's going to be a complicated process to get you back to normalcy", Lawrence Mayor Dan Rivera said. It makes them feel special that people out there care about us - that the Red Sox were taking cash donations at the games, that stuff is really great.More news: Toyota Yaris GR Sport revealed ahead of Paris debut
Baker declared a state of emergency Friday and said New England-based Eversource would replace Columbia Gas as the lead utility in the recovery efforts. Baker said New England-based Eversource would replace Columbia Gas of MA.