A faulty extension cord touched off the horrific blaze that killed five children inside a Pennsylvania day care center two months ago, investigators revealed.

Flames tore through Harris Family Day Care, claiming the lives of children 8 months to 8 years old, on Aug. 11 in Erie, Pennsylvania, about 130 miles north of Pittsburgh, authorities said.

The blaze has been formally declared by accident by investigators from the Bureau of Alcohol, Tobacco, Firearms and Explosives, the Allegheny County Fire Marshal's Office and the Erie Police and Fire Departments.

"Based upon data collected during this investigation and the subsequent analysis of that data, it is the combined opinion of the fire scene investigation team that the fire was caused by an electrical failure associated with a routinely used extension cord" in the living room, according to an ATF statement released on Thursday.

"After a complete analysis of all the data collected, the fire was determined to be accidental."

No criminal charges are pending, ATF Special Agent Charlene Hennessy said.

"The integrity of the wiring was compromised," Hennessy told NBC News on Friday. "There was a faulty wire inside of the extension cord."

Four of the young victims were siblings and children of Lawerence Park firefighter Luther Jones and certified nursing assistant Shevona Overton.

Jones was out responding to a separate call early that morning when the Erie Fire Department battled flames at the day care, while Overton was working an overnight shift.

Their children were Jaydan, about 8 months, Ava, 4, Luther Jr., 6, and La'Myhia, 8.

Jones said at the time that if the home had more smoke detectors, there might have been a better chance for everyone inside to escape and "my kids would be here today."