Lies — or mistakes? South Philly double-murder trial hinges on testimony from teenagers.

Andrew Zanghi admits that when he first spoke to homicide detectives in October 2017, he didn’t tell them that he saw Brandon Olivieri fatally shoot two teens, including Zanghi’s friend, on a South Philadelphia street corner.

It wasn’t until two days later, Zanghi testified Tuesday, that he told police in a follow-up interview that he knew Olivieri was the gunman.

Does that mean Zanghi, now 18, intentionally lied to the police? Or did he simply omit information the day he watched his friend die because he was afraid to say too much about what he saw?

That question hung over the opening day of testimony in Olivieri’s murder trial, during which Zanghi’s testimony took center stage.

And credibility issues are likely to emerge again this week, with prosecutors poised to call more teen witnesses in an attempt to prove that Olivieri killed 16-year-olds Salvatore DiNubile and Caleer Miller during a shooting at 12th and Ritner Streets.

“It’s not that I lied,” Zanghi testified under cross-examination from Olivieri’s attorney, Robert Mozenter. “I just left stuff off.”

Common Pleas Court Judge Barbara A. McDermott, aware of the hostility among relatives and friends of the victims and Olivieri, warned spectators to be on their best behavior, and Tuesday’s proceedings were held in a larger-than-usual room to accommodate a bigger audience.

The room was packed to near-capacity with relatives and friends of the three youths, but any signs of conflict appeared to be muted. Some gallery members cried during opening statements by attorneys.

During his remarks, Assistant District Attorney David Osborne told jurors that the shooting began because Olivieri had been spoiling for a fight. Hanging with three friends after school, Osborne said, the South Philadelphia teen and his buddies, including Miller, decided to wander their neighborhood streets looking for scores to settle when they made their way to 12th and Ritner Streets.

When Olivieri saw DiNubile, Osborne said, he thought he recognized DiNubile as someone who had embarrassed him in a previous fight. Olivieri, according to Osborne, then took out a .45-caliber handgun and pulled the trigger while struggling with DiNubile over the gun.

“He knew that it wasn’t going to be like last time,” Osborne said. “He knew he wasn’t going to be embarrassed.”

One shot hit DiNubile, while another hit Miller by mistake, the prosecutor said.

Mozenter, Olivieri’s attorney, countered during his opening statement that no physical evidence showed his client as the gunman, and that the witnesses expected to testify included several teens who lied to police or in court or cut deals with prosecutors to avoid being charged. He also said there was “no evidence” that Olivieri knew DiNubile, and said Olivieri had no motive to commit the killings.

The case against Olivieri, Mozenter said, “is built on inconsistencies, chaos, and confusion.”

Zanghi testified that he was with DiNubile and several other teens at 12th and Ritner when Olivieri, Miller, and two other teens approached them. Zanghi said he knew Miller from a previous school, and that he and Miller spoke briefly as Olivieri stared at DiNubile.

According to Zanghi, he heard DiNubile say: “Aren’t you that kid?” To which Olivieri replied: “Yeah, what do you want to get into?” Zanghi said he then saw Olivieri pull a handgun from his waistband, and saw DiNubile charge toward the gun. During a struggle over the weapon, Zanghi said, several shots went off and most teens scattered.

DiNubile and Miller were declared dead that night. Zanghi said he spoke with detectives that night but was afraid to identify Olivieri to police as the gunman.

Mozenter, however, sought to paint Zanghi as a liar whose testimony was unreliable — either by misleading the police that night, or by giving them a faulty identification days later.

Testimony in Olivieri’s trial is expected to continue Wednesday.