Denison first tried to log into the ISO's computer system, but was unsuccessful because his computer privileges had been suspended, investigators said. Denison broke a glass cover that protected an emergency shut-off button, meant for use in case of fire or other calamity, according to the release.
Denison allegedly went home after shutting off the power to the computers, and told a friend the next morning that he had pressed the emergency button and had tried to "shut off the power grid," according to prosecutors.
The ISO manages high-voltage lines owned by Pacific Gas and Electric Co., Southern California Edison and San Diego Gas & Electric Co. The April 15 outage disrupted CalISO communications for about two hours, leaving the grid vulnerable to electricity shortages. The ISO used back-up systems to reconnect to the energy market.
Denison is scheduled to be sentenced by U.S. District Judge Garland E. Burrell Jr. at 9 a.m. on Feb. 29. The maximum penalty for attempting to damage an energy facility is five years imprisonment, a $250,000 fine and a three-year term of supervised release. Denison originally had also been charged with making a bomb threat.
The case was investigated by the Federal Bureau of Investigations's Joint Terrorism Task Force, composed of federal, state and local law enforcement agencies.