A pipeline controller working at a console in Columbus, Ohio, noticed the pressure increase in a pipeline in Lawrence, Massachusetts, one of the three towns where the fires occurred, Sumwalt told CNN's Alison Kosik.
Speaking in Lawrence Sunday morning, Gov. Charlie Baker said teams have completed assessing and turning off all 8,600 of the affected gas meters.
Firefighters and gas workers returned Saturday morning to a commercial area on the south side of Lawrence where they were seen opening manholes, testing gas levels and trying to gain access to businesses.
A preliminary investigation determined the blaze on Diamond Street was unrelated to the gas leaks that forced thousands of residents from their homes, Lawrence Fire Chief Brian Moriarty said.
CreditSights Inc. analysts said Friday in a note that the MA incident "appears to have been caused by the utility working on the gas lines immediately before the explosions occurred".
At least 25 people were treated for injuries. Electricity was restored to almost all homes and businesses, but gas service will remain shut off while officials continue investigating what caused Thursday's explosions and fires.
Salisbury nerve attack suspects say they were in United Kingdom as tourists
While they acknowledged being the pair seen in images released by Scotland Yard, the men did not provide proof of their names. RT ran part of the interview on Thursday morning, in which Petrov said: "We are those shown to you in the (CCTV) pictures".
Witness accounts suggest the incidents began at about 16:30 local time (20:30 GMT).
Electric power is being restored and will be available to all customers by noon on Sunday, Eversource said on its website.
"We're very interested to understand the operations of Columbia Gas", he said. The remaining displaced residents, which officials say are in the thousands, likely stayed with friends and family, Red Cross spokesman Jeff Hall said.
Leonel Rondon, 18, was killed after a chimney that had been blown off a home in one of the explosions struck a auto in Lawrence, CNN affiliate WHDH reported. He later died at the hospital, authorities said.
Do not attempt to use any gas appliances until gas service has been safely restored by the gas company.
Columbia Gas, owned by NiSource Inc., has been linked to previous accidents in other states, The Boston Globe reported Friday. The company a subsidiary of NiSource, a utility company that serves more than three million customers in seven states.