An NTSB pressure test identified a leak in the main gas pipe that runs under Park Avenue.
It is an eight inch cast iron main that is partially 127 years old, although portions of it have been more recently replaced and are made of plastic. The NTSB found the leak by pumping tracing gas into the main.
"It indicates that the main did not hold pressure, which indicates that there was a leak in the main," said gas industry expert Bob Ackley of Gas Safety USA.
The NTSB says they are not drawing any conclusions as to what caused the explosion, simply releasing information that they've learned.
The leak was located adjacent to 1646 Park Avenue, one of the buildings that collapsed. It is unclear if the leak was at the feeder line to the building or in between the feeder lines.
Another new development late Tuesday, as we learned part of a cracked water main pipe one building down from the explosion had been removed and sent to NTSB labs as evidence for further analysis.
"If the water main broke, and washed away the fill that was surrounding the gas pipe, it could have contributed to the failure of the gas pipe," said Ackley.
Wednesday will mark a week since the explosion that destroyed two five-story buildings and killed 8 people.
Early on, a leak in the old cast iron piping has been among the leading suspected causes but even with Tuesday's added proof that it had a leak, no one is willing to draw a conclusion.
"I don't have enough information to make that determination. Typically if you have cast iron bell and spigot joints that they will leak," said Ackley.
Pressure testing of the service lines to buildings on Park Avenue adjacent to the destroyed buildings continues with no significant findings to date. ConEdison and the city are working to restore gas service to the adjacent buildings.
Meanwhile, the last efforts have been made to clear the area of splintered debris. Some of it was thrown from nearly rooftops.
This community is also healing together.
"It's a sad situation that it happened. And I hope the best for the families who lost their homes. But things do happen. But you can see the community pulling together and that's one good thing about it," Fred Broughton said.
They held one another outside the Ortiz Funeral Home Monday night, tears and anguish over their sudden loss. They were so overwhelmed, so overcome with grief, paramedics had to treat some.
They came to remember George Amadeo, just 44 years old, he was one of the eight killed in the explosion.
Friends and loved ones paid their respects to Andreas Panagopoulos in Astoria on Sunday night.
The 43-year-old musician also worked online from the East Harlem apartment he shared with his wife of eight years.
Authorities have identified the eighth and final victim of the explosion as 34 year old Mayumi Nakamura of Japan. She was traveling alone in the U.S. and had no relatives here, according to the Japanese consulate.
The medical examiner classified the eight deaths as accidents. Five victims - Griselde Camacho, Carmen Tanco, Andreas Panagopoulos, George Amadeo and Rosaura Barrios - died from combinations of blunt trauma injuries to the head, torso and extremities, said medical examiner spokeswoman Julie Bolcer. Two others, Rosaura Hernandez and Jordy Salas, died from smoke inhalation and burns. Nakamura died from thermal injuries, the medical examiner said.
The blast erupted about 15 minutes after someone from a neighboring building reported smelling gas, authorities said. The National Transportation Safety Board, which investigates pipeline accidents, said Friday that underground tests conducted in the hours after the explosion registered high concentrations of natural gas.
More than 60 people were injured in the explosion and more than 100 others were displaced.
Two of those injured, an East Harlem woman and a high school student riding on a passing bus, have filed the first lawsuit against the city over the explosion.
Fire and utility officials said that if the buildings were plagued in recent days or weeks by strong gas odors, as some tenants contend, they have no evidence anyone reported it before Wednesday. An Associated Press analysis of the city's 311 calls database from Jan. 1, 2013, through Tuesday also found no calls from the buildings about gas.
(The Associated Press contributed to this report)