It took jurors less than 48 hours to find Gallo guilty of three counts of second-degree murder after the crash that killed Adenhart, 20-year-old Courtney Stewart and 25-year-old Henry Pearson.
As the jury's decision was read, family members of the victims started sobbing.
"We've been waiting to hear those words for a year and a half," said Stewart's mother, Carrie.
About 20 friends and family members of the victims were in the courtroom to hear the verdict.
Gallo had a blood-alcohol level of .19 when he ran a red light at a Fullerton intersection and T-boned the vehicle that was driven by Stewart in April 2009.
Jurors agreed with the prosecutor, who argued that Gallo showed conscious disregard for human life. Gallo was driving drunk and speeding.
Video from a bar showed Gallo and his step-brother drinking several beers and shots before the crash
He was also found guilty of driving under the influence, causing bodily injury to a third passenger. Jon Wilhite, 24, of Manhattan Beach, suffered an internal decapitation and is still recovering.
Wilhite, a former California State University at Fullerton baseball player was hugged by friends and family outside the courtroom.
Adenhart had pitched six scoreless innings at a home game the night he was killed in the crash.
Though his sentencing is pending, Gallo could spend up to 50 years in jail.
"Obviously there are no winners in this situation, but the familes are satisfied with the verdict," said Pearson's father, Nigel.
"I hope this is a step in the right direction," Wilhite's father, Tony. "People out there will think before they drink."
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