Robert Martinez, 22, was found guilty Friday of fatally shooting Steven Cerna, 21, at point-blank range in 2015.
Jurors deliberated for just 90 minutes before returning their verdict.
During closing arguments Friday, the focus of the defense and the prosecution was on the state's key witness, Larry Isaac, who is the defendant's uncle.
Isaac, 31, testified Thursday that Martinez admitted to killing Cerna after luring him to a drainage ditch known as Hell's Gate on the city's near North Side on Feb. 20, 2015.
Isaac said Martinez told him that the killing was a revenge slaying carried out because he suspected that Cerna's relatives were involved in the murder of one of his friends.
Isaac, who is jailed on kidnapping charges in another case, testified against Martinez as part of a plea agreement.
His sentence in the kidnapping case, as a result of the plea deal, will be reduced.
"We can't corroborate even his reasons for being up here, let alone anything he has to say," defense attorney Leland McCrae said during closing arguments on Friday. "But it was riveting."
Prosecutor Kristina Escalona countered McCrea's argument, saying Isaac testified for selfish reasons.
"He knew he had information, and he wanted to use it to help himself. But he knew he had credible information," Escalona told jurors. "We should stand for the truth, no matter who tells it."
Testimony in the punishment phase resumes Tuesday in Judge Melisa Skinner's 290th District Court.
Martinez could face a maximum sentence of life in prison.