Three environmental activists were indicted on charges that they helped vandalize a U.S. Forest Service research station in northern Wisconsin, prosecutors said Tuesday.

A recently unsealed indictment said members of the Earth Liberation Front and Earth First damaged the property in Rhinelander in 2000 because they erroneously believed that scientists were performing genetic research on trees.

Katherine Christianson of Santa Fe, N.M., Aaron Ellringer of Eau Claire, Wis., and Bryan Rivera of Olympia, Wash., were charged with conspiring to damage government property and damaging government property. They face up to 15 years in prison if convicted.

Prosecutors said Christianson, Rivera and two others cut down 500 research trees and used spray paint and etching cream to vandalize government vehicles with ELF references, including: “ELF is watching the U.S. Forest Service.” The indictment noted $500,000 in damage.

Ellringer was their driver, prosecutors said.

The environmental activist groups, which have used arson and vandalism in protests, view that research as damaging to the environment, prosecutors said. The vandals planned the attack to coincide with protests at the International Society for Animal Geneticists in Minneapolis, the indictment said.

The attack set back an ongoing research project designed to make certain species of trees grow faster and healthier to improve their efficiency as an energy source, said Tom Schmidt, a Forest Service official in St. Paul who oversees the Rhinelander station.

Schmidt said the project does not involve genetic research and instead uses traditional plant-breeding techniques.

“Unfortunately, they were misinformed on that,” he said. The attack has prompted the Forest Service to improve security at the Rhinelander facility, which has about 20 full-time employees.

“It’s really sad when something like that happens. People put their lives into it, and it was for a really good thing,” Schmidt said. “We took a blow to the belly and kept on going forward ... We’re just pleased that it appears justice will be served.”

ELF took responsibility, describing it as an attack on bioengineering. In a statement, the group said: “We are everywhere and nowhere and we are watching. For wildness and an end to industrial society.”

The FBI arrested Rivera, a 31-year-old man also known as “Brian Lefey” and “Rat Dog,” last week in Washington state. He is expected to be transferred to Wisconsin to make his initial appearance in federal court next month.

Christianson, 27, and Ellringer, 35, both made their initial court appearances Tuesday. U.S. Magistrate Judge Stephen Crocker ordered their release pending trial, which is scheduled for Dec. 1.

Lawyers for the three did not immediately return phone messages Tuesday.