A hearing has been set for Nov. 5 to schedule a new trial.
Alverez, 56, faces a charge of first-degree felony murder in connection with the May 2011 death of 29-year-old Jorge Veracruz.
Monday, on the first day of Alverez's trial in 3rd District Court, a defense attorney said Alverez was protecting himself from a perceived threat.
Alverez and Veracruz were part of a group who were hanging out and drinking in Riverside Park, 700 N. 1400 West, on the evening of May 5, 2011.
The two men began arguing with each other and soon there was talk of fighting, said prosecutor Bradford Cooley. Alverez made mention of the .22-caliber semiautomatic gun he was carrying and Veracruz walked away.
But as the man walked down a path along the Jordan River, the prosecutor said, Alverez fired at least three shots.
One shot struck Veracruz in the back of the right arm. A second went into the right side of his back. A third shot hit the left side of Veracruz's back, piercing his spleen, stomach and aorta before stopping in his lung.
Alverez's defense attorney said the man believed Veracruz was going to rob him and fired only when he saw the man reaching for something in a bag.
"Frank didn't know Jorge. He could have been reaching for anything. … Frank was afraid for his life. He was afraid for his safety," defense attorney Adam Alba said. "He acted only to protect himself, and he was justified."