After a burst of bullets from a fully automatic AK-47 rifle killed a 25-year-old woman as she drove down a Vallejo street with her boyfriend, police identified everyone involved in her death — including the gunman.

But a year later, the case is over. And no one will be held accountable for the slaying of Gina Estevez in her tan Mercedes-Benz.

Solano County prosecutors charged the boyfriend with murder, arguing under California’s provocative act doctrine that he had put her in danger by bringing her to a violent confrontation, while concluding that the shooter — a suspected gang member — acted in self-defense. He was granted immunity to testify as a key witness.

But the strategy broke down this week when a jury, after deliberating for less than an hour, acquitted the boyfriend, 27-year-old Rewia Beamon.

“I didn’t feel any genuine remorse from either party. Neither one of them is innocent,” said Christina Bayardo, 26, a friend of the victim who attended preliminary hearings in the case as well as the trial. “Gina died for absolutely no reason. She was just caught in the middle.”

After the verdict, which was handed down Tuesday, the district attorney’s office said the shooter, 20-year-old Marlon Williams, will not be charged with murder, manslaughter or any lesser offense in connection with the death of Estevez, who lived in Daly City.

Asked about the outcome, Solano County District Attorney Krishna Abrams said, “We always respect the jury taking their time and hearing all the evidence.”

Prosecutors said Beamon had brought his girlfriend to a gunfight, creating the situation that led to her death. But the failed case has baffled Beamon’s public defender, raised eyebrows among criminal justice experts, and outraged Estevez’s friends and relatives.

“If you openly admit to taking someone’s innocent life, how do you get immunity?” said Crystal Sliva, 29, the victim’s best friend. “How do you not get charged?”

She and others noted that under California law, the district attorney’s office could have gone after both Beamon and Williams.

The shooting happened on July 7, 2015, when Beamon asked Estevez to drive him to his ex-girlfriend’s house on Broadway Street in Vallejo, according to authorities and friends. There, Beamon and the ex-girlfriend got into a heated argument, and Williams — a friend of the ex-girlfriend’s family who was inside the house — went to the attic to get the AK-47.

What happened next is disputed. Prosecutors argued, based on Williams’ recollection, that Beamon made threats, brandished a gun and fired it.

But Beamon’s attorney, Tamani Taylor, said there was no evidence showing Beamon had a gun in his car, let alone his hand. No shell casings or bullet holes were connected to Beamon, she said. The prosecution and the defense disagreed on whether gunshot residue was later found on Beamon’s hands.

As Beamon and Estevez drove away, Williams fired four shots from the porch. Estevez, in the driver’s seat, was struck in the back of the head, while Beamon was hit by shrapnel. Beamon took over the wheel, driving about a quarter of a mile before he got out and begged neighbors for help.

According to the defense, Williams went into hiding for so long that his mother filed a missing person’s report. After being arrested for alleged identity theft weeks later, he told Vallejo police he had been aiming at Beamon in self-defense.

Williams’ attorney, Carol Long, said Friday she could not discuss the case.

The district attorney’s office opted to try the case under the provocative act doctrine, which allows prosecutors to file murder charges against people who don’t physically commit killings but somehow incite them. For instance, an armed bank robber can be charged in the death of an accomplice gunned down by a guard who acts in self-defense.

But Taylor said the death of Estevez didn’t fit the doctrine, and questioned whether Williams’ account was his own.

“He was spoon-fed this self-defense-type scenario and then he parroted it back to police,” she said. “It was clear from listening to the interview that they spoon-fed him the way they wanted this case to be presented, who they wanted to show was the victim.”

Some former prosecutors, too, said giving the shooter immunity was questionable.

“Prosecutors have to be particularly careful when their star witness is someone they’re giving some type of deal,” said Darryl Stallworth, a former Alameda County deputy district attorney now working as a criminal defense lawyer. “If that’s your star witness, as you might imagine, that’s going to be the face of your case. Here, it looks like that was the biggest problem.”

Stallworth and others said provocative-act murder cases are always challenging.

“You’re holding someone for first-degree murder who didn’t pull the trigger,” said Steve Clark, a legal analyst and former Santa Clara County deputy district attorney. “Jurors are a little squeamish about that.

“If he did indeed fire an AK-47 into a fleeing vehicle, that’s not a reasonable self-defense,” Clark added. “Certainly it doesn’t seem like a good outcome for the district attorney’s office. The shooter isn’t held responsible, and the guy who provoked him walks.”

The victim’s father, Ramon Estevez, said he went to some hearings but had to stop because listening to testimony was too painful. He said both men should have been charged.

“It’s really hard on me and my family,” he said. “I don’t have words to think of what to say.”

Estevez’s loved ones questioned why Williams was not at least charged for possessing or using an illegal assault rifle.

“That’s certainly not a self-defense gun,” said friend Elena Murphy, 24. “That’s a kill-everyone gun.”

Kimberly Veklerov is a San Francisco Chronicle staff writer. Email: kveklerov@sfchronicle.com Twitter: @kveklerov