Witness says fight broke out before fatal ’08 Chelsea club shooting

“At the beginning, I thought the gun was not a real gun,’’ Diaz said in Spanish, through an interpreter. “This person was firing and firing a gun, and I didn’t see anyone fall down; that’s why I thought it wasn’t real.’’

But seconds later, Diaz said, he realized the weapon was real.

Holding his hands seemingly a foot apart, he described the size of the gun. “It was a black gun, looked just like in the movies, a very big pistol.’’

Diaz said that as he ran for the exit, he saw Jesse Camacho, the weapon in his hand, shoot a man.

“And then he shot him two more times as he was on the ground,’’ Diaz said. “Pop, pop, that’s when I realized that the gun he had was real, because the person he shot was lying on the ground with his eyes wide open.’’

Camacho, 22, is on trial, charged with first-degree murder in the killing of 27-year-old Jeff Santiago of Everett inside King Arthur’s Lounge shortly after midnight on Jan. 24. He also faces two counts of attempted murder. He has pleaded not guilty. Yesterday, his attorney, Willie Davis, said in a brief interview at the lunch break that his client acted in self-defense.

Camacho sat stoically as Diaz, who was an acquaintance of his, delivered dramatic testimony that had many jurors on the edge of their seats.

At one point, Assistant District Attorney Patrick Haggan asked Diaz to stand up and demonstrate Camacho’s alleged actions. Diaz, dressed in a white shirt and khaki pants, stood in front of the jurors, fashioned his right hand like a pistol, and pointed to the floor about 3 feet in front of him. “Pow, pow, pow,’’ he said loudly in English.

Diaz’s testimony was preceded by Camacho’s former girlfriend, who said he was “just acting normal’’ when she gave him a ride from his house in East Boston to a friend’s house in Revere on an early January morning more than two years ago.

But prosecutors say that Camacho had just fatally shot Santiago and almost killed two other men, leaving the club in chaos.

Evelyn Chabout, 23, who had been dating Camacho for about seven months prior to the shooting, gave an often-tearful testimony. After she dropped him off, Chabout said, he called her hours later and still seemed calm. Camacho would soon go on the run, hiding out in New Hampshire and Mexico, prosecutors said. Chabout often took his calls and called him long-distance, but did not see him again until yesterday, when she walked into the eighth-floor courtroom and past her former boyfriend on her way to the witness stand.

Chabout spoke after a morning of testimony by two forensics specialists, who detailed the ballistics evidence found in the club and the bullet-torn sweater worn by Santiago.

At one point, Christopher Dougherty, a ballistics expert with the Massachusetts State Police, held up a bag containing the twisted bullet fragment taken from Santiago’s body.

Camacho spent five months in a Mexican jail before he was brought back to Boston to be arraigned, authorities said.

Brian R. Ballou can be reached at bballou@globe.com.