(NewsNation) — San Jose, California, resident Peter Karasev was arraigned in the Northern District of California on charges of destroying energy facilities and using fire or explosives to commit a federal crime.

Karasev, a 36-year-old engineer, was indicted in October on charges that include knowingly and willfully damaging the property of two energy facilities and using fire and explosives to commit a felony. He pleaded not guilty to the charges.

Prosecutors said Karasev damaged two PG&E transformers in San Jose on Dec. 8, 2022 and Jan. 5, 2023. In a memorandum asking the court to detain Karasev pending a trial, prosecutors detailed the attacks, which occurred early in the morning in commercial areas. The attacks left 1,500 residential and business customers without power.

“These charges make clear that those who attack our country’s critical infrastructure will be met with the full force of the Justice Department,” said Attorney General Merrick B. Garland. “We have charged Peter Karasev with bombing two energy transformers in Northern California, leaving more than 1,500 households and businesses in the San Jose community without power”

Prosecutors allege Karasev spent the months leading up to the attacks building and experimenting with homemade explosives. According to court documents, law enforcement found improvised explosive devices in various stages of construction, multiple firearms, other weapons and more than 300 pounds of materials used to make explosives in Karasev’s home when he was arrested. Prosecutors said he was also making methamphetamine in the home.

Karasev was arrested in March and was held on state charges related to the same incidents before being transferred to federal custody. If convicted, he faces a mandatory minimum of 10 years in prison and a maximum penalty of 20 years in prison, a $250,000 fine and three years of supervised release for each count.