A 42-year Columbia Gas employee said his bosses ignored repeated warning about potential safety issues.
But not federal investigators, who used the retired utility worker's testimony to help build their criminal case.
On Wednesday, Bart Maderios reacted to the federal criminal charges against his former employer.
"I cried for days. It devastated me for months," Maderios said of the September 2018 catastrophe. "There isn't a day where I don't think about the tragedy that happened in the Merrimack Valley."
Maderios was manager of the Meters and Regulation Department at the company. His primary job was to oversee pressure control of the natural gas system in the Lawrence area.
The series of explosions and fires in 2018 showed the devastating consequences of what can happen when pressure surges out of control.
"It was preventable. It was human error," Maderios expressed.
The manager abruptly retired several months prior to the tragedy, saying he was forced out the door after a lengthy career because he was too outspoken about safety concerns.
Maderios first spoke to the NBC10 Boston Investigators in the wake of the tragedy, detailing his efforts to sound the alarm about lack of resources and cutting corners to boost the company's bottom line.
"My major concern was the lack of people to do the job safely," Maderios recalled.
Following the NBC10 Boston interview, there was swift reaction from Massachusetts lawmakers. Maderios said he also spoke with federal investigators and provided grand jury testimony.
His attempts to alert company officials to potential safety problems were detailed in federal court documents, where he was identified as "M&R Leader-1."
"M&R Leader-1 described the need for more resources as 'urgent' and warned there were potential consequences for not adding resources," the federal complaint said.
Despite the federal action, Maderios said he was still disappointed that no individual employees will face criminal charges.
During a Wednesday press conference, U.S. Attorney Andrew Lelling acknowledged that conclusion would be more satisfying to the public, but said it wasn't a case prosecutors could prove.
"There simply was no one single individual here who rose to the level of an individual federal crime," Lelling said.
That explanation did not sit well with Maderios, who believes he provided enough evidence for certain employees to be held accountable for not following safety procedures.
"Why do you have rules and regulations? You have them because people die and people get hurt," he said.