DENVER -- A man accused of dragging a dog to its death at the Colorado National Monument pleaded guilty Thursday in federal court.

Steven Clay Romero , of Mesa County, admitted to aggravated animal cruelty in connection with the death of a German shepherd named Buddy on Dec. 30, 2009.

Romero told the judge that he has an "anger problem" and is taking medication for it.

While stressing that there is no federal sentencing guideline for that charge, attorneys had agreed to a sentence, based on state law for a corresponding class-six felony, of up to three years in prison and a fine of up to $100,000.

Sentencing was set for July 30, at 9 a.m.

National Park Service personnel found the body of the dog with a rope around its neck, on the side of Rim Rock Drive. Tracks in the snow indicated the animal had been dragged behind a vehicle for at least two miles.

Surveillance video taken at the park's Fruita entrance showed a double-cab pickup entering the park at 2:18 a.m. on Dec. 30, with a dog in the truck's bed. The same truck was videotaped exiting 12 minutes later without the dog.

An investigation revealed that Buddy was stolen from a Delta residence. A witness wrote down the license plane number of the pickup truck that was used and that led investigators to Romero's home where dog prints were seen in the front yard.

A neighbor told investigators he saw Romero drive away with a dog in the bed of a pickup truck at about 2 a.m. on Dec. 30. Park rangers were given permission to search Romero's home and said they found rope similar to the rope found around the dog's neck.

Before Romero's arrest, officials posted photos of the dead dog on the park's Web site in hopes that people would recognize the animal and report the person (or persons) who committed "this horrific crime upon a defenseless animal."

Rangers interviewed Romero's sister, Melissa Marie Lockhart, who said she saw the dog in the home and said that her brother said he was going to kill the dog.

Lockhart was charged for her attempt to cover up the dog’s slaying. Her case is still pending. If convicted, Lockhart faces not more than three years in federal prison, and up to a $250,000 fine, or both.

Steve Leber, the owner of the dog, said he has not replaced Buddy and he probably can't.

After the guilty plea, Leber said justice was served and he was overwhelmed with the response to Buddy's death.

“It’s amazing. It’s amazing that many people care," Leber said. "To some people it was just a dog, apparently. But to a lot of them he was something special.”

A Facebook group called "Demand Justice For Buddy" has more than 260,000 members.