TUCSON — U.S. Border Patrol Agent Nicholas Corbett took the stand in U.S. District Court on Tuesday to tell jurors what happened when he fatally shot an illegal immigrant last year, saying he did so in self-defense.

But he was unable to recall or explain some parts of the story.

Francisco Dominguez-Rivera was shot on Jan. 12, 2007.

On Jan. 12, 2007, while Corbett was apprehending four Mexicans who had illegally entered the United States between Naco and Douglas, he killed Francisco Dominguez-Rivera with his service pistol. The prosecution claims the slaying was unjustified, while the defense says the action was self-defense.

Corbett was one of two witnesses the defense called on Tuesday. It was the first time he’s spoken publicly about the incident. He did not speak with investigators about the incident, but did speak to other Border Patrol officials about it, according to reports.

On Tuesday, the prosecution also called two rebuttal witnesses. The jury then heard closing arguments and began to deliberate for about 30 minutes before going home for the evening.

Corbett testified that he pulled up near Dominguez-Rivera, his two brothers and one brother’s girlfriend, put his Chevy Tahoe in park and saw the victim bend down and pick up a rock that he described as about the size of a softball but not as rounded.

Corbett, who is about 6 feet 4 inches tall and who weighed 250 pounds at the time, opened the door and exited the vehicle. He drew his weapon, headed around the back of the vehicle and confronted Dominguez-Rivera, who was 5 feet 3 inches tall and weighed 145 pounds. He told the victim in Spanish to “sit down,” but Dominguez-Rivera began walking toward him until they got within 3 feet of each other.

The agent said Dominguez-Rivera had an expression of “hatred” on his face.

The defense showed the jury an artist’s rendition of how the defendant and the victim were standing at the time of the shooting. In the drawing, Corbett is holding the gun in his right hand and pointing it down and toward the left side of the victim’s body. Dominguez-Rivera is holding a rock in his right hand, and Corbett is stretching out his left arm to block it.

Corbett denied statements by eyewitnesses that he shot the victim from behind or while the victim was kneeling down. He also denied he struck the victim in the back of the neck with his gun or pointed the gun while he was driving his vehicle.

Sean Chapman, the lead defense attorney, asked Corbett why he shot Dominguez-Rivera, and he replied, “Because he was going to smash my head in with a rock.”

Three Border Patrol agents testified last week regarding what Corbett said took place when he shot Dominguez-Rivera. One other agent testified during a preliminary hearing in August. They gave varying accounts as to what happened, but none gave a description that matched Corbett’s testimony.

During cross-examination, Grant Woods, the lead special prosecutor, asked Corbett if all four of them were “wrong” about what occurred.

“Yes. They had the wrong impression,” Corbett replied. And, Woods countered, “You are the only one who had it wrong.”

John Maciulla, a criminalist employed by the Arizona Department of Public Safety, was called by the prosecution as a rebuttal witness. He had testified last week that the bullet fired by Corbett entered the victim under his left arm, but it made a hole through the chest area of his sweater. Attorneys suggested that the sweater was moved to the left side either because one of the victim’s brothers pulled on his sleeve or if Corbett grabbed the victim and shoved him down.

On Tuesday, Maciulla said that if Corbett were pushing his left arm against the right shoulder of the victim, then the sweater would move in the opposite direction of the left armpit.

During another part of his testimony, Corbett said he did not announce the shooting over his radio. But, last week, Steve Berg, the Border Patrol agent who was the first to arrive on the scene, testified that he heard a “shots fired” call from Corbett via his hand-held radio. Woods asked Corbett if he recalled hearing that testimony from Berg, but said he could not remember it.

Corbett also was unable to say which direction his body was facing at the time of the shooting after Woods asked him several times to describe and explain the situation.

Also Tuesday, the defense called Elmer Pellegrino, director of the police academy at Fullerton College in California, who testified that officers involved in shootings may experience framing or tunnel vision. As a result, they may distort some facts as a result of undergoing the stressful situation.

Pellegrino said he was retained by the defense at $250 per hour, plus $125, and he had worked a total of 35 to 40 hours.

The other rebuttal witness that the prosecution called was Justice of the Peace David Morales, who presided over the preliminary hearing in August in Bisbee. He testified that he did not observe anybody coaching the three eyewitnesses during their testimony.

His statement contradicts a claim from Dove Haber, a public information officer for Border Patrol, that she saw Oscar de la Torre, the Mexican consul in Douglas, make gestures in order to lead the witnesses. But on cross-examination from Chapman, Morales acknowledged that his attention was not completely focused on members of the audience in the court room.

Last week, prosecutors made the court aware that they wanted to present evidence of prior bad acts committed by Corbett that shows violence or propensity toward violence. On Tuesday, Judge David Bury refused to allow the prosecution to do so basically because the evidence was not disclosed prior to the start of the trial.