Two men have been arrested and charged with vandalizing electrical substations in Washington state, attacks that left thousands without power over the holidays, and one suspect told authorities they did it so they could break into a business and steal money, U.S. authorities said Tuesday.

Matthew Greenwood, 32, and Jeremy Crahan, 40, both of Puyallup, were arrested Saturday and set to appear in U.S. District Court in Tacoma on Tuesday.

A newly unsealed complaint charged both with conspiracy to damage energy facilities, and it charged Greenwood with possession of a short-barreled rifle and a short-barreled shotgun. Cellphone location data and other evidence tied them to the attacks on the four substations in Pierce County, the complaint said.

The attacks on Dec. 25 left more than 15,000 customers without power. Officials have warned that the U.S. power grid needs better security to prevent domestic terrorism and after a large outage in North Carolina last month took days to repair.

According to the complaint, Greenwood told investigators after his arrest that the two knocked out power so they could burglarize a business and steal from the cash register. The business was not identified in the complaint.

“We have seen attacks such as these increase in Western Washington and throughout the country and must treat each incident seriously,” Seattle U.S. Attorney Nick Brown said in a news release. “The outages on Christmas left thousands in the dark and cold and put some who need power for medical devices at extreme risk.”

It was not immediately clear if the men had attorneys who might speak on their behalf.

The four substations targeted were the Graham and Elk Plain substations operated by Tacoma Power and the Kapowsin and Hemlock substations operated by Puget Sound Energy. The complaint said transformers at the Tacoma Power substations would have to be replaced and damage was estimated to be at least $3 million.

According to the complaint, the pair hit the first three substations early on Christmas Day, then struck the last — the Kapowsin substation — that evening. In each case, they used bolt cutters to access the properties and manipulated switches to knock out power. At the Kapowsin substation, their actions cause arcing and sparking, the complaint said.

Greenwood and Crahan were identified as suspects because location data showed cellphones linked to them to be in the vicinity of all four incidents, FBI Special Agent Mark Tucher wrote in the complaint. Agents surveilled them from Dec. 27 to Jan. 3 and they appeared to be sharing a home in Puyallup, he said.

“The substations are spread out over dozens of miles; the attacks occurred early in the morning and in the evening; and the first and fourth attacks were separated by over twelve hours,” the complaint said. “This makes it at least unlikely that an individual would simply happen to be at all four locations around the times they were each vandalized.”

When he was arrested, Greenwood had several articles of clothing that matched images of one of the suspects in surveillance images, and agents found him to have two unregistered short-barreled weapons, the complaint said.

Conspiracy to attack energy facilities is punishable by up to 20 years in prison. Possession of an unregistered firearm is punishable by up to 10 years.

At least four electrical substations were targeted in earlier attacks in Oregon and Washington beginning in late November. Attackers used firearms in at least some of the incidents and some power customers in Oregon temporarily lost service. In one of the attacks, two people cut through a fence surrounding a high-voltage substation and then shot several pieces of equipment.

The utilities affected in those cases — Portland General Electric, the Bonneville Power Administration and Puget Sound Energy — said they were working with the FBI.

(AP)