And watching the spectacle from a nearby car were the animal-rights activists who started the blaze, police say.

One has already pleaded guilty; the second was charged with arson.

Joshua Stephen Demmitt, 18, made his first appearance Tuesday in U.S. District Court, dressed in a shirt and tie, and accompanied by his mother and attorney.

The U.S. Attorney's Office anticipated that Demmitt would plead guilty, but instead his attorney asked for a one-week delay. U.S. Attorney for Utah Paul Warner later issued a news release vowing to file more serious charges if Demmitt does not plead guilty by Friday.

Harrison David Burrows, 18, admitted two weeks ago that on July 8 he and Demmitt attacked the Ellsworth Farm, where animal husbandry experiments are conducted. Burrows said the attack was committed "on behalf of the Animal Liberation Front," according to a statement read when he pleaded guilty.

Burrows said he poured gasoline on cardboard and lit it on fire, while Demmitt ignited two tractors.

The ALF, which is considered a domestic terrorist group by the FBI, claimed responsibility for the arson and two earlier vandalisms at the Ellsworth Farm, through e-mails sent to The Salt Lake Tribune.

Warner said Tuesday that Demmitt and Burrows were behind each incident.

On May 16, at least three people removed six rabbits and seven birds from the farm, writing "ALF" and "Don't Play God."

On May 29, someone poured iodine on the barn floor and put sugar in a gas tank of a pickup. "ALF" and other graffiti were spray painted.

Similar graffiti, including "You are the terrorists" and "This will never end," were found at the scene of the July 8 fire.

Burrows is expected to be sentenced Jan. 10. Demmitt's next court appearance is scheduled for Tuesday. If convicted, Demmitt would serve five to 20 years in a federal prison.

mcanham@sltrib.com