The announcement of a verdict came at about 6 p.m., roughly four hours after the jury was given the case.
The conviction carries with it a mandatory life sentence.
"I cannot even begin to tell you how difficult this has been for me and the personal responsibility that I will struggle with; the fact that I knew Marni Yang to begin with. I can't find the words to convey the regret that I'll have the rest of my life," Gayle said outside the courtroom.
Reuter's family thanked prosecutors for the they did to paint Yang as a callous killer. The defense team did not make a public comment.
In their closing arguments earlier in the day, prosecutors said the shooting of Rhoni Reuter was "a well-planned, thought-out execution." They made the case that Yang was so preoccupied with Gayle that she murdered Reuter on the morning of Oct. 4, 2007.
But the defense contended that Yang was a victim too. Attorney William Hedrick told jurors last week that at the time of the slaying, Gayle was seeing 18 or 19 different women.
Gayle later admitted he had a sexual relationship with Marni Yang and that they had sex the night before the murder.
Yang didn't testify during her trial.
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