Michael Robles said he grabbed his friend from behind to try to stop him from beating a taxicab driver who was already on the ground from earlier kicks and punches.
But his friend, Kilani Derego, broke free.
"He went back to the cabdriver, and he kicked him one to two times in his face," he said.
Robles, 19, and Derego, 18, are each facing a charge of second-degree murder for the May 1, 2010, fatal beating of taxicab driver Charlys Ty Tang.
Tang died from head injuries. May 1, 2010, was his 41st birthday.
Robles is on trial in state court. He took the witness stand in his own defense Tuesday.
Derego is scheduled to go to trial in October.
Robles said Tang had just taken him and Derego to Waipahu from Waikiki when Derego and Tang got into an argument.
He said Derego had earlier instructed him to get out of the cab and run without paying when they arrived in Waipahu.
Robles said he did run when the cab stopped in the Waipahu Times Super Market parking lot. But when he turned back, he saw that Derego and Tang were involved in a scuffle outside the cab.
"While I was walking back, that’s when I saw Kilani throw the first punch. And it landed in the guy’s facial area. And then the guy went down," he said.
Robles said Derego continued punching Tang, who was on the ground holding on to Derego’s legs.
He said he stepped in between Derego and Tang, and kicked Tang twice in the shoulder to try to break Derego free, but Tang held on to one of Derego’s legs. He said Derego pushed him out of the way and continued punching Tang. Even after Tang released Derego, he said Derego "whacked (Tang) twice more in the facial area," causing Tang’s head to bounce off the ground.
Robles said he and Derego are childhood friends from Hawaii island. He said that at the time of the beating, they were both residents of a Hale Kipa therapeutic group home for at-risk youth in Manoa, where they practiced mixed martial arts and Thai kickboxing.
Robles said he sneaked out of the home just hours before Tang’s beating to meet Derego in Waikiki, even though according to the prosecutor, Hale Kipa records indicate he was in the group home at the time of Tang’s beating.
Correction: Michael Robles and Kilani Derego were residents of a Hale Kipa home for at-risk youth in Manoa. An earlier version of this story incorrectly said they were part of a Kahe Mohala program.