CHICAGO, Illinois (CNN) -- Mike Mette has been a Chicago police officer for almost four years. But now, as a result of a fistfight one night in Dubuque, Iowa, he is a convicted felon.

Mike Mette, a Chicago police officer, says he acted in self-defense when he punched Jake Gotthard, a student at the University of Dubuque.

Mette has been sentenced to almost five years in prison after Dubuque County Judge Monica Ackley found him guilty of assault causing serious injury. Mette says he's been wronged.

"I was arrested for self-defense ... I was defending myself," he said.

Mette's saga started in October 2005 after a night of drinking in Dubuque, where he was visiting his brother Mark. After the bars closed, Mette and his crew made their way to an after-hours party thrown by Jake Gotthard, a student at the University of Dubuque.

According to court documents, Mette and his friends entered the house party, but decided to leave without paying the required $5 entry fee when they saw the room was mostly empty. Gotthard became angry, and with the help of his roommate, began chasing Mette down the street. Gotthard claims someone in Mette's group had stolen his cell phone and he wanted it back. Exactly what happened to the cell phone is still unclear.

The altercation continued a block and a half down the street and eventually ended up in front of the house of Mette's brother. Fight could land cop in prison »

"That's when Mr. Gotthard hit me. He hit me with two fists like this, straight into the chest," Mette said. "He was yelling about his cell phone, telling me if he didn't get his cell phone back he was going to beat the crap out of me. He hit me several more times and then I pushed him away from me. It wasn't until after the third time is when he came back at me again and that is when I struck him."

When police arrived, they found Gotthard lying on the ground with bruises and lacerations on his face, cheek, nose, chin and forehead. Mette, who had blood on his shirt and whose knuckle was bruised and cut, was arrested and charged with a felony.

"[Gotthard] had bruises on the side of his neck, his arms, his elbow, his shoulders, on his back, that were simply not consistent with Mr. Mette's version that he only struck him once," said Assistant County Attorney Tim Gallagher.

Dubuque doctors testified the injuries were consistent with someone who had been stomped and kicked. But a doctor testifying for Mette's defense rejected the Dubuque findings. He said all those injuries could have come from Mette's single punch and the impact from falling on the sidewalk.

Gallagher said the decision to prosecute Mette was a tough one.

"It's never an easy situation when someone is sentenced to prison, particularly when it's a police officer that we have to rely on," he said. "But we can't allow individuals to be given certain privileges because of their occupation."

The case spawned a battle between newspaper columnists in Chicago and Dubuque.

"Mette played baseball in college. But what's happening to him isn't about Iowa baseball mythology. It doesn't smell of corn. It stinks of the pig barn," wrote Chicago Tribune columnist John Kass. He chalks the judge's decision up to small town politics.

In a reply, a columnist for the Dubuque Telegraph Herald wrote that Kass is a "legendary muckraker" who is "training his scorn" on Ackley, the judge.

Mette is currently on unpaid leave from the Chicago Police Department and is appealing his case. He will begin serving his five-year sentence in November. E-mail to a friend

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