Pacific Gas and Electric Company is offering a $250,000 reward for information leading to an arrest and conviction in the attack on a California substation last year.
In April 2013, snipers unloaded on the Metcalf substation, then vanished before police arrived.
The military-style attack blasted 17 giant transformers, which power parts of Silicon Valley and resulted in more than $15 million in damage.
The people responsible also cut fiber-optic lines, knocking out phone and 911 service in the area.
AT&T is offering its own $250,000 reward.