Updated 09/28/11 – 9:55 p.m.

CHICAGO (CBS) — A Cook County jury has convicted a 22-year-old reputed gang member of killing a Chicago police officer two years ago.

Shawn Gaston, 22, was convicted of first-degree murder in the death of Officer Alejandro “Alex” Valadez on June 1, 2009.

Jurors reached their verdict late Wednesday evening, just a few hours after beginning their deliberations, following a weeklong trial.

alejandro valadez Reputed Gang Member Convicted Of Killing Chicago Cop

Chicago Police Officer Alejandro Valadez (Credit: CPD)

Valadez was 27 years old when he was shot to death in 2009. He had been on the force for only three years and was working undercover duty on the South Side on June 1, 2009, investigating reports of gunfire when Gaston allegedly gunned him down on the 6000 block of South Hermitage Avenue.

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“We are very pleased with the verdict,” Cook County State’s Attorney Anita Alvarez – who personally prosecuted the case, said after the verdict. “We think it’s really important, number one, for the family of Officer Valadez for them to find some peace and some justice in the verdict tonight.”

“We also think it’s extremely important for all the citizens of the city of Chicago to know that there are people like Officer Valadez who are out there every day,” Alvarez added. “This man actually put his life on the line for them and he lost his life.”

Officer Valadez’s sister, Brenda, thanked the jury for what she called a “just verdict.”

“Even though the defendant was found guilty, this was not a happy occasion for us because this verdict does not bring Alex back,” Brenda Valadez said. “My parents will never see their last born son again. My siblings and I will never share another holiday. My nieces and nephews no longer have their silly uncle that made them laugh. My son will not have his godfather to guide him.”

“But worst of all, my nephew who was born three months after my brother was murdered will never know what his daddy’s hugs and kisses feel like. His daddy will not be there on his first day of school,” she added. “His daddy will not be there to cheer him at tee ball or guide him through life and share all those wonderful memories that wonderful and loving fathers share with their sons.”

Prosecutors alleged that, as Valadez and his partner were questioning several residents about the reported gunfire, a vehicle drove up and Gaston opened fire, striking Officer Valadez once in the leg and once in the head.

Gaston was also found guilty of the attempted murder of an Englewood resident Valadez was interviewing when he was shot.

During the trial, jurors saw and heard Gaston confessing to the killing when he was questioned by police.

Gaston said on tape that he and a friend had just gotten tattoos from “a big fat white dude” and were driving near 60th Street and Hermitage Avenue when someone fired shots at their car, the Sun-Times reported.

Gaston said he went home and got a gun he had hid under a neighbor’s porch, and returned, opening fire into a crowd, the newspaper reported.

Gaston and Kevin Walker, who was the driver, were arrested about an hour after the shooting. They were also responsible for the original gunfire Valadez was investigating, officials said. Walker and Gaston are both charged with first-degree murder.

Prosecutors said a bullet casing was found stuck on the car that Valadez was in. The murder weapon and two other guns were found in the car, which belonged to Gaston’s mother.

But defense attorneys said Gaston’s DNA wasn’t found on the murder weapon and that the wound to Valadez’s head appears to have come from above, making it impossible for their client to have shot Valadez from a moving car.

Defense attorneys suggested that a couple of rogue officers might have planted the guns which were found in the vehicle after it was towed from the scene and then moved a second time.

But Alvarez dismissed those claims.

“We believe that, obviously, this verdict is based on the evidence that we presented. We felt very strongly in the evidence that we presented. I don’t believe there’s any evidence to support any of the theories that the defense put forward,” she said.

Gaston faces 61 to 101 years in prison, according to Alvarez.

Walker still awaits trial in the case, as does a third man, Christopher Harris, who was arrested and charged later.

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