GRANTS PASS, Ore. —  Two people have been charged in a federal investigation of a string of Northwest arsons claimed by the shadowy radical groups Earth Liberation Front and Animal Liberation Front, authorities said Wednesday.

Jonathan Paul, 39, was arrested Tuesday on charges that he helped firebomb a horsemeat packing plant in Redmond, Ore., in 1997, said Diane Peterson, spokeswoman for the U.S. attorney's office in Portland.

Suzanne Savoie, 28, remained at large, Peterson said. She was charged with serving as a lookout for the 2001 firebombing of the offices of a lumber mill in Glendale, Ore.

Each suspect faces up to 20 years in prison and a $250,000 fine.

The ALF has claimed responsibility for the slaughterhouse fire. It caused an estimated $1 million in damage, but 100 horses in nearby corrals survived.

Paul allegedly set the fire with the help of a woman, who was unnamed in the criminal complaint.

The ELF claimed responsibility for the lumber mill fire.

The two suspects bring to nine the number of people charged in a series of arsons from 1996 to 2001 in Oregon and Washington. They include torchings of two lumber mill offices, a tree farm, an SUV dealer and two federal research labs.