Boy Testifies in Slaying : Trial: He singles out his mother’s boyfriend as the man who beat his infant sister to death.

A 5-year-old boy, seated on a blanket and a pillow so he could see better from the witness stand, pointed to Steven Delgado on Tuesday as the man who he watched beat his infant sister to death in a night of terror last September.

In a quiet courtroom, Johnny Ortiz, at times fidgeting with a paper cup, spent more than an hour testifying in the murder trial of Delgado, who was romantically linked with the boy’s mother.

“Steve came in, he hit Amanda and hit me, and that’s how Amanda died,” the boy testified.

Delgado, 22, is on trial for the slaying of 11-month-old Amanda and an assault on Johnny last Sept. 26 in the apartment of the boy’s mother in Santa Ana. If convicted of first-degree murder, Delgado could be sentenced to a maximum of life in prison.

Neither prosecutors nor police have suggested a motive for the killing. But Manuel Ortiz, the father of both children, said he believed that Delgado killed his daughter because she was interfering with Delgado’s romantic relationship with the mother, Elizabeth Ruiz.

In initial questioning by Deputy Dist. Atty. Robert C. Gannon Jr., the boy identified Delgado without hesitation.

“She was on the floor, and I was in the bed,” he said, describing the moments before the attack that left his sister dead. “She was just going to come up to bed, and I helped her up.”

The boy, who is now in the custody of his father, told jurors that he was in bed with his sister when Delgado entered the room, threw Amanda against a wall, beat her repeatedly with his fist, and then hit him in the mouth.

His testimony matched a videotaped statement he made to police last year.

An autopsy found that injuries to the girl’s abdomen were the primary cause of death. Two skull fractures and multiple chest bruises also were found, Gannon told jurors in last Wednesday’s opening arguments.

Despite close questioning by defense attorney Frederick L. McBride that produced apparent inconsistencies in his testimony, Johnny maintained his composure.

McBride focused his questioning on the “two bad men” who Johnny first told authorities had entered the apartment and struck him that evening.

Asked whether he had told the police any lies, Johnny responded, “No.”

Santa Ana Police Officer Michael D. Fuller testified last week that he found no signs of forced entry into the apartment.

At one point, the boy also acknowledged that he had told police that Delgado did not kill his sister. But when asked whether that was the truth or a lie, the boy said he did not remember.

Last week, McBride tried unsuccessfully to have the boy’s testimony excluded from the trial. He contended that an interview conducted following the investigation was “so suggestive that the child’s memory was distorted.”

Gannon said Delgado and Ruiz, who worked together at a Santa Ana insurance firm, became romantically involved five months before her child’s death. Delgado had a key to Ruiz’s North Durant Street apartment and had known her since childhood, he said.

At times, both McBride and Gannon appeared frustrated with Ruiz’s testimony. Last week in the courtroom of Orange County Superior Judge Ragnar Engebretsen, both questioned her repeatedly about inconsistent accounts she has given of the events that occurred on the night her daughter was killed. Ruiz testified that she was not present at the time of the slaying.

Because they were witnesses in the trial, neither she nor Johnny’s father was present in the courtroom Tuesday while he was testifying except when he was asked whether he could identify the person who committed the crime.

At that point, both mother and father were brought into the courtroom and seated in the front row. Gannon declined to explain why.

After the boy identified Delgado, the parents were escorted out by bailiffs. Gannon said the unusual action had been agreed upon in advance.

Testimony by young children is not unusual in criminal cases, said James G. Enright, the county’s chief deputy district attorney.

“They have several young victims testify in child molestation cases,” Enright said. “The main determination is that they can recall (what happened) and they know what it is to tell a lie.”