The NTSB concludes there were two main causes of the explosion: the failure of a defective fusion joint installed by Con Edison in 2011, and a breach in the sewer line that went unrepaired by the DEP since 2006 that washed away the ground supporting the gas main.
Both New York City and Con Edison are disputing portions of the NTSB's findings.
The NTSB left no doubt that city neglect of its sewer and an shoddy work by an uncertified Con Ed worker caused the March 12, 2014 explosion that leveled two apartment buildings.
"Its antecedents had been building for years," said NTSB Chairman Christopher Hart. "In particular, the inadequate preparation of the service tee resulted in incomplete fusion welding to the gas main in 2011, which caused the joint to be defective".
But the NTSB also faults the city for neglecting to fix a hole in the sewer line, causing water and debris to erode the ground around the gas line causing it to crack at a defective weld.
The Board says the city knew for years the sewer was a problem.
"They conducted street repairs in 2004, o7, 09, 2010 203 and three days before the incident so obviously some erosion going on there," said Robert Sumwalt of the NTSB.
The city says the sewer was too far away to cause the pipe to crack but the NTSB says with no sewer breach there would have been no deadly blast.
Still, the NTSB says the proper weld would also have prevented the explosion but Con Ed says the cracked weld wasn't at fault.
"We think the faulty joint happened after excavation. Many things we found after the explosion indicated to us fusion came apart after the explosion," said Con Ed's Mike Clendenin.
"Are you saying Con Ed has no blame here?," we asked.
"No not saying that. There is plenty for everyone to learn from this episode," he said.
The NTSB earlier said it had found a leak in a cast iron gas main from 1887.
Sections of the pipe and a cracked section of an 1897 water main were shipped to the NTSB lab in Washington for further examination.
In a statement, a city spokesman maintained it was the fault of Con Edison, saying "I would underscore that the NTSB's recommendations were nearly all focused on Con Ed and the defective fusion joint that they said caused the explosion. The City firmly believes - and the facts back us up -- that sewer damage did NOT play a role."
Con Ed also released a statement: "To be clear, not all of the participants involved in this investigation reached the same conclusion concerning the sequence of infrastructure failures that led to the explosion. We all agree, however, on the importance of doing everything in our control to prevent a tragedy like this from happening again."
Still searching for answers are the families of the eight victims.
"I am trying to follow what they are saying on the investigation, but at the same time it is hard," said the wife of a victim, Liseth Perez. "I just don't want to know sometimes."
While this day was tough for her, she still follows from her offices at El Diario the hearings into the explosion that took the life of Andreas Panagopoulos, her loving husband of 13 years.
"My husband is not going to be back, and the lives of all the other seven people who died that day are not going to be back. But we need to know what's happened," she said.
Andreas was at home in the couple's East Harlem apartment when their four story building along Park Avenue near 116th Street suddenly exploded, reducing it to smoldering rubble, killing Andreas and seven other residents.