The shooting was captured on surveillance video. First you can see a streak of light, which may have been from a flashlight, followed by the muzzle flash of rifles and sparks of bullets hitting the chain link fence around the substation.
It happened April 16, 2013, just before 1 a.m. Someone dropped into an underground vault and cut AT&T fiber optic cables, temporarily knocking out 911 service and phone service. Then, the snipers opened fire on the substation, shooting for 19 minutes. They knocked out 17 transformers that supply power to Silicon Valley.
When police arrived, the suspects were gone, and more than 100 fingerprint-free shell casings were found at the scene.
"This wasn't some haphazard type attack from four or five guys drinking beer one night. Looks like it was a planned attack," said former FBI Agent Rick Smith.
In that respect, Smith agrees with Jon Wellinghoff, former Federal Energy Regulatory Commission chairman, who spoke out on the issue Wednesday, calling it an act of terrorism. Wellinghoff told the Wall Street Journal the attack was "the most significant incident of domestic terrorism involving the grid that has ever occurred" in the U.S.
Wellinghoff, who was in office during the incident, said he reached his conclusion after consulting with Defense Department experts about the attack.
But no one claimed responsibility for the sabotage, which is something that a terrorist would most likely do. And taking down a power station would not necessarily evoke terror.
No one has been arrested in the case.
Wellinghoff worries it was a rehearsal for a bigger terror plot. And, if replicated across the country, it could take down the U.S. grid and black out much of the country.
But Smith says if it was terrorism, there would be evidence.
"There would have to be some information from an informant, terrorist group informant, whether it domestic or international, that some group was responsible for it," he said.
"So, the feeling is this may have been a preparation for an act of war," said Rich Lordan, a senior technical executive at the Electric Power Research Institute. He says the execution of the attack is unprecedented.
"They knew what to cut in the communications systems. They knew where to cut it. They knew what equipment to go after. And they also knew how to get out of there before police and fire came."
Officially, the FBI is saying this was not terrorism, but the bureau and PG&E say they are still investigating.
KGO-TV reporters Katie Marzullo and Vic Lee and The Associated Press contributed to this report.