From multiple points to the northeast and northwest of the substation, it was easy to see the transformers lined up inside, about 150 yards away. I parked and climbed a hill, and the only thing slowing me down was thistle. I had brought my binoculars; I trained them on an area inside the wall. I had an unobstructed view of the bushings sticking out of the transformers like lightning-struck hair, the vulnerable cooling fins jutting out of their side bulk.

Incredibly, there are five gun ranges in the hills around the substation, including a 200-yard range meant for high-powered rifles. As I scanned the facility with my binoculars, I could hear them all. From a pistol range I heard an announcement, “OK, shooters, we’re in a safe-fire zone,” followed by a flurry of two-beat reports. It was not difficult to imagine what the valley would have sounded like the night the snipers opened fire.

In 2013, the Department of Homeland Security sent a delegation to utilities around the country, urging them to increase security at their substations. “We did a nationwide tour to alert owners and operators about the vulnerabilities,” Caitlin Durkovich, then the assistant secretary for infrastructure protection, told me, but with more than 200,000 miles of high-voltage transmission lines and roughly 55,000 substations spread across the country, “there is awareness that you can’t protect everything.”

The year after, NERC published a “reliability standard” for utilities, requiring them to assess their substations and prepare a plan to defend them from physical attacks. How the utility would do that, however, was left unspecified. “Identify what are the physical security issues that you need to manage, and then manage them” is how Lauby described the standard to me, though NERC does regularly audit compliance. Whatever upgrades the utilities have done, Wellinghoff told me, they may not have outpaced the development of new threats. “We have a whole new situation,” he said, “and that is the emergence of this very, very sophisticated drone warfare.” He added that the grid had changed in the years since 2013, though, and it was possible that new transmission lines added resilience to the system.

The F.B.I. last commented on the Metcalf attack in 2014, when an official again suggested that it was the work of a disgruntled employee, an idea Wellinghoff calls “ridiculous.” (It would need to have been two disgruntled employees, in any case, because the cover to the vault holding the substation’s communications links was too heavy to lift single-handedly.) One PG&E executive called the shooting a “dress rehearsal” for future attacks, and indeed, in the past decade, dozens of facilities — in Arkansas and Oregon, Florida and Washington — have been targeted, often using the same tactic as the one seen in 2013: puncturing the cooling system and letting the oil drain out.