Updated 01/26/12 – 9:30 p.m.

CHICAGO (CBS) — A Cook County courtroom packed with Chicago police officers erupted in cheers Thursday afternoon when a jury returned a guilty verdict against a 40-year-old man charged with killing Officer Nathaniel Taylor in 2008.

Jurors deliberated for about two hours before finding Lamar Cooper guilty of first-degree murder in Taylor’s death.

Taylor, 39, was gunned down while assisting with the execution of a search warrant on Sept. 28, 2008.

LISTEN: WBBM Newsradio’s John Cody reports

nathaniel taylor 0123 Admitted Drug Dealer Convicted Of Killing Cop In 2008

Chicago Police Officer Nathaniel Taylor (Credit: Chicago Police Department)

Cooper was accused of killing the 14-year police officer when Taylor and a team of drug officers tried to serve Cooper with a search warrant.

In closing arguments, the defense acknowledged Cooper was a drug dealer and that he shot Taylor, but argued Cooper could only see a vague shape approaching his car and could not see Taylor’s police shield hanging on a chain around his neck, so Cooper thought he was being robbed and fired in self-defense.

But Assistant Cook County State’s Attorney James McKay ridiculed the defense’s claim, saying drug dealers know how police operate and know narcotics officers often wear street clothes instead of their uniforms.

McKay said, even if Cooper couldn’t see Taylor’s police shield and thought he was being robbed, he could have fled, called 911 or fired a warning shot into the air.

“This was a sneak attack by this drug dealer on one of our heroes,” McKay said.

Cooper had already done time for attempted murder of another police officer in 1990 and now faces a possible life sentence for Taylor’s murder.

Dozens of police officers and family members filled the courtroom after learning a verdict had been reached and erupted in cheers after the guilty verdict was announced.

One of Cooper’s attorneys was infuriated by the courtroom outburst.

“That’s inappropriate behavior in a public courtroom,” Assistant Public Defender Susan Smith said.

But a friend of the slain officer took comfort in the display.

“Now he can rest in peace,” Angel Gogins said.

Cook County State’s Attorney Anita Alvarez said she is “content” with the mandatory life sentence now awaiting Lamar Cooper. She thinks the death penalty, which has been abolished in Illinois, would have been more appropriate.

Cooper’s trial started Monday at the Cook County Criminal Courthouse and wrapped up Thursday. Jurors began deliberating around 1:30 p.m. Thursday. Around two hours later, it was announced a verdict had been reached.

Taylor’s partner, Lem Miller, fought back tears as he testified at the start of the trial about seeing Taylor get shot in the head, chest and arm as he walked up to Cooper’s car.

Taylor and Miller were assigned to conduct surveillance on Cooper’s home on the morning of Sept. 28, 2008, in preparation for a team of officers to serve a search warrant on the home at 7 a.m.

When Cooper pulled up in front of his house around 5:30 a.m., Taylor and Miller were told to detain Cooper to keep him from entering his home, as police believed there were weapons, dogs and children inside.

Miller testified that, as Taylor approached Cooper’s car, Taylor identified himself as a police officer. The next thing his partner heard was two or three rapid shots. Then he saw Taylor go down.

Miller said he drew his gun and fired at Cooper 10 times, hitting him nine times before calling for help on his radio and checking on Taylor.

Taylor, 39, died hours later during surgery at Advocate Christ Medical Center in Oak Lawn.

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