Around 1 a.m. on April 16th last year, a team of attackers cut phone lines and took out 17 power transformers at a PG&E substation south of San Jose, nearly causing a blackout throughout Silicon Valley. According to the former chairman of the Federal Energy Regulatory Commission, it was the "most significant incident of domestic terrorism" involving the nation's power grid. No one has been charged or arrested in the attack.

The Wall Street Journal, broke news of the attack today, pieced together a timeline of events that unfolded in the middle of the night, just yards from Highway 101:

The attack began just before 1 a.m. on April 16 last year, when someone slipped into an underground vault not far from a busy freeway and cut telephone cables.

Within half an hour, snipers opened fire on a nearby electrical substation. Shooting for 19 minutes, they surgically knocked out 17 giant transformers that funnel power to Silicon Valley. A minute before a police car arrived, the shooters disappeared into the night.

The team of gunmen knew what they were doing in the caper too: they targeted oil-filled cooling systems that bled out until the transformers overheated and crashed rather than shooting up the explosion-prone transformers themselves. The crash triggered an alarm at a PG&E control center 90 miles away, but police on the scene around 1:51 a.m. couldn't get past a locked fence and assumed everything was fine.

Electric-grid officials, meanwhile, scrambled to avoid a blackout by re-routing power from other plants in Silicon Valley. It still took utility workers nearly a month to bring the Metcalf Transmission station back online.

Nearly a year later and FBI officials in San Francisco tell the WSJ, the Bureau doesn't think a terrorist organization was behind the attack, but they are "continuing to sift through the evidence." PG&E's official statement claimed it was the work of vandals, but made no mention of the nearly 100 fingerprint-free shell casings that were found at the scene. Former FERC chairmain Jon Wellinghoff, meanwhile, saw fit to go public with the details after military experts confirmed the scene looks like a professional job.

At a recent security conference, one former PG&E vice president of transmission put it bluntly: "This wasn't an incident where Billy-Bob and Joe decided, after a few brewskis, to come in and shoot up a substation," Mark Johnson said in a presentation. "This was an event that was well thought out, well planned and they targeted certain components." PG&E won't discuss any further details, fearing potential copycat bands of Billy-Bobs and/or unnamed terrorist organizations.

Transmission stations like Metcalf are crucial links in the power grid, which has utility officials scared that anyone could come along and cause a blackout like the one that crippled the North East in 2003. Although Wellinghoff is sounding the alarm here, more level heads from the not-for-profit North American Electric Reliability Corp. claimed in a very customer support-sounding response that even if several substations crashed, most people would get their power back in a few hours. Which will be helpful when you want to read about it online a year later.