SPRINGFIELD, Mass. (WHDH) -- On Sunday officials announced that the natural gas explosion in downtown Springfield Friday was the fault of a utility worker who accidentally punctured a high-pressure pipeline while looking for a leak. But while the explosion was due to human error, officials are now saying it was not one person’s fault.

First, there was a gas leak. Then, a worker looking for the source accidentally triggered this massive explosion.

"We have determined that human error, not a fault in the gas infrastructure is the cause of what the explosion was,” said the state fire marshal, Stephen Coan.

But it wasn't that worker at fault. Markings that were supposed to show the location of the high-pressured gas line were incorrect.

"His metal probe inadvertently punctured the high pressure gas line at the foundation of the building,” said Coan.

After puncturing the pipe, the worker immediately called the fire department. Along with police, the responders quickly evacuated the area.

Moments later, the explosion leveled the 4-story strip club and damaged about 42 surrounding buildings, including a daycare center and several apartment buildings.

"The investigative team believes that the gas from the leak entered the building around the pipe and at some point reached the correct explosive level of gas and air which ignited by many possible ignition sources inside the building,” said Coan.

Three buildings have already been condemned and engineers are still inspecting the others to see if they are safe for residents to return.

Most of the injured were utility workers and firefighters who ducked for cover seconds before the explosion.

They suffered minor injuries and all 20 people have since been treated and released.