The April 16, 2013, attack had not been widely publicized until The Wall Street Journal reported new details in a story on Wednesday. The attack reportedly started when at least one person entered an underground vault to cut telephone cables, and attackers fired more than 100 shots into Pacific Gas & Electric's Metcalf transmission substation, knocking out 17 transformers. Electric officials were able to avert a blackout, but it took 27 days to repair the damage.
The FBI doesn't think the incident was a terror attack, an agency spokesman told the Journal. However, Jon Wellinghoff, chairman of the Federal Energy Regulatory Commission at the time, disagrees.
Wellinghoff, a now-retired George W. Bush appointee, called it "the most significant incident of domestic terrorism involving the U.S. power grid that has ever occurred."
No arrests have been made in the case. But the Republican-led House Energy and Commerce Committee said Wednesday that lawmakers continue to follow the probe and that protecting the grid remains a top priority.
"We are aware of the attack and continue to monitor the investigation closely," a committee spokeswoman told FoxNews.com. "Committee staff has been briefed by agency officials and industry representatives. The security and reliability of the grid is a pressing concern, and we will continue our work to mitigate all emerging threats."
Wellinghoff, who spoke to the Journal, based his conclusion that this was terrorism on the analysis of experts he brought to the crime scene. The analysis pointed to the shell casings having no fingerprints and evidence that the shooting positions had been pre-arranged.
Wellinghoff went public with the story after briefing federal agencies, Congress and the White House, citing national security concerns and fear that electric-grid sites don't have adequate protection.
In addition, retired PG&E executive Mark Johnson said at an industry gathering a few months ago that he feared the attack was a dress rehearsal for a larger event, according to the Journal.
The utility company responded to a call seeking comment by referring FoxNews.com to a statement from the Edison Electric Institute.