OAKLAND -- The facts that routinely accompany the violence that plagues Oakland's inner-city streets were on display in a courtroom Tuesday as a murder trial against a teenager began.

It includes underage boys using guns to solve squabbles. Witnesses refusing to speak to law enforcement out of fear of street retribution. And, sadly, the dead body of an 18-year-old found lying on a sidewalk in front of an apartment building, shot to death in the middle of the day.

"Unfortunately, this is not something that is unusual," Deputy District Attorney Amilcar Butch Ford told the jury. "These teenage boys are out at that apartment just playing with guns like it's a game."

That "game" resulted in Casey Turner, who was 15 years old at the time of the incident, facing life in prison for allegedly killing James Allen Jr., 18, and wounding two others during a gunbattle on March 27, 2010.

Turner, now 18, was charged as an adult.

According to Ford, Turner shot Allen and the two others who were with him as they exited from a walkway of an apartment building at 2124 90th Ave. in East Oakland.

At the time, police said the shooting was the result of a spat Allen and Turner were having over a girl Allen once dated.

Ford said he will prove to the jury that Turner was the teen who opened the gunbattle as he waited across the street for Allen and his friends to leave the apartment building. While Allen also fired a gun during the battle, Ford said Turner fired first, making him guilty of first-degree murder.

But the case against Turner relies on testimony from witnesses, many of whom do not want to cooperate with investigators, Ford said. Many of the witnesses, Ford said, have been forced to appear in court under threats of arrest and are fearful of being labeled "snitches" for cooperating.

"The reason they are nervous is because they are not supposed to tell what happened," Ford said.

One such witness testified Tuesday but said he couldn't remember key details of the shooting. The 17-year-old, who Ford requested not be identified, had previously told police that Turner shot first and that his friend Allen fired back with a gun Allen had showed him earlier that day.

But on the witness stand, the 17-year-old said he couldn't remember if Allen had a gun or who shot first.

"I don't know where the bullets were coming from, I just heard gunshots and I ran," the teenager said. "I ran because a bullet ain't got no name on it."

The witness, who is also named in the criminal complaint filed against Turner as being a victim of attempted murder, said he believed he was shot at because the hoodie he was wearing had a bullet hole in it. But the witness said he threw the hoodie in the garbage.

Other witnesses expected to testify in the case include a woman who lived in the apartment building and who told police she saw Turner run from the scene after the shooting.

Another witness is Allen's friend Burnett Raven, who was also shot in the gunbattle and identified Turner as the shooter. Raven, 19, however, will not testify during the trial because he is on life-support at a hospital after being shot recently in an unrelated incident.

Yet, Ford said, he will still be able to prove the case to the jury.

"The issue is who shot first," Ford said. "Casey Turner started the fight."

Turner's attorney, Darryl Billups, declined to give an opening statement Tuesday.

Contact Paul T. Rosynsky at 510-208-6455. Follow him at Twitter.com/insidechambers.