UPDATED 08/10/12 12:14 p.m.

CHICAGO (CBS) — A 25-year-old teacher in the Chicago Public Schools allegedly called police overnight and admitted to beating his dog to death in the East Lakeview neighborhood.

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Derek Fierro is charged with aggravated animal cruelty, police say.

Police say at 3 a.m. Friday, they received a call from Fierro, of 500 block of West Roscoe Street – just east of Broadway. He said he got angry and beat his dog to death, then placed the animal’s body in the trunk of his car, police said.

Officers came to the scene, and Fierro allegedly gave them the garage code to the building, his car keys, and permission to open the trunk. A dead yellow male dog was inside, police said.

Fierro was arrested and continued to apologize at the police station, police said.

Fierro allegedly told officers that he had arrived home to discover that the dog had eaten every piece of paper in the house, and pooped on himself.

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Fierro said he tried to put the dog in the bathtub to wash him, and became angry when the dog kept struggling, police said.

At that point, Fierro became angry and began punching the dog to the point where he died, police said.

Fierro is a 4th-grade teacher at the Eugene Field Elementary School, at 7019 N. Ashland Blvd. in the Rogers Park neighborhood.

“We are aware of the allegations,” a CPS spokesman said, and the case is “under investigation by the Office of the Inspector General.”

A bond hearing for Fierro is set for later Friday.

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The Sun-Times Media Wire contributed to this report.