VISTA -- Figuring out what would possess three teenage gang members to open fire on Oceanside policeman Dan Bessant -- in an unprovoked ambush -- takes an understanding of the gang culture, a prosecutor told a jury Tuesday.

Killing a policeman is a criminal pinnacle, Deputy District Attorney Tom Manning said, and on the streets it brings respect to the gang and to the individual killer. It was the whole point of the slaying.

"It enhances their status in the warped subculture of the gang mentality," Manning said in his closing arguments in the first of at least two expected murder cases arising from the slaying of Bessant on Dec. 20, 2006.

Penifoti "P.J." Taeotui, who was 16 at the time of the killing, has pleaded not guilty to murder and other charges.

After four weeks of testimony, Manning laid out his theory of the case to a jury of three men and nine women. The panel is expected to begin deliberating Wednesday after Taeotui's defense attorney, Wil Rumble, makes his closing arguments. Rumble has said his client was not at the scene.

Taeotui, now 18, is a documented member of a gang that claims turf in the area where the killing happened, not far from Camp Pendleton's back gate.

Prosecutors say Taeotui and two fellow young gang members had been drinking and playing with guns when they spotted police activity at a traffic stop and decided to take aim.

Bessant was shot through the heart after stopping to see if a fellow officer needed assistance during a routine and unrelated traffic stop.

The prosecution contends the bullet that killed Bessant came not from Taeotui, but his friend Meki Gaono, who was 17 at the time.

Prosecutors also say Gaono was peering through a rifle scope when he allegedly shot at Bessant, and that Taeotui and a third teen simultaneously fired handguns at the officer.

Although Taeotui's bullets did not hit Bessant, he is culpable in the slaying because he aided and abetted Gaono, Manning told the panel as he asked them to convict the teenager of first-degree murder.

If Taeotui is convicted of murder and special circumstances, including the killing of a peace officer, he faces life in prison without the possibility of parole. Because he was a juvenile at the time of the crime, he is not eligible for the death penalty.

Gaono is set to go to trial in January, and prosecutors say he has confessed to firing the fatal bullet. The third teenager who prosecutors suspect took part in the ambush faces no charges at this time. A judge dismissed the case against him for lack of evidence.

Manning contended during his closing arguments that the teenage trio targeted Oceanside police at random because word had spread through the gang that authorities were cracking down. Oceanside officials had started warning some of the documented gang members and their families that they could face civil actions that might see them kicked out of their homes if the gang trouble didn't stop.

That threat -- seen by the gang as harassment -- played into the mindset of Taeotui and his friends, young gang members bent on proving themselves and boosting the street cred of their gang, which at the time had more than 90 documented members, Manning said.

Taeotui was "entrenched in the gang lifestyle," Manning said. "That is why this crime happened. That is why a police officer was murdered."

Manning laid out Bessant's final moments, and suggested the 25-year-old officer -- who was married and the father of a two-month-old son -- died moments after the shooting, as he sat slumped against a police cruiser.

Bessant's parents, seated in the front row of the crowded courtroom, gripped hands. With her free hand, Bessant's mother dabbed at her eyes with a tissue.

Taeotui, seated at the defense table, wore a dark suit and had his long hair pulled into a bun at the nape of his neck. During Manning's arguments, which lasted more than four hours, he did not appear to look up much from papers in front of him at the table.

There are no witnesses who will say they saw Taeotui pull the trigger on the .22-caliber revolver that prosecutors say he used.

But people in the neighborhood that evening testified they saw a person who may match Taeotui's description at the mailbox on which Gaono allegedly steadied himself to get a good shot.

The most damning evidence may be Taeotui's own words to friends in the wake of the shooting, prosecutors say.

One former gang member testified about two weeks ago that Taeotui gave him details a day after the slaying while Taeotui was laying low.

The witness testified that Taeotui told him Gaono had the officer in his rifle sights when Gaono said something to the effect of "I can get a shot from here," to which Taeotui allegedly responded "Are you sure?"

And once Gaono fired, Taeotui lifted his revolver and joined in the shooting, according to the witness who said Taeotui confessed to him.

Contact staff writer Teri Figueroa at (760) 740-5442 or tfigueroa@nctimes.com.