As 18-year-old Chancey Luna, shackles on his wrists and ankles, stood in court waiting to learn he would be sentenced to life in jail without the chance of parole a prosecutor noticed something.

Written eloquently in black pen on the back pocket of Luna’s orange jumpsuit were three words: “Crip for Life”.

Theories of why Luna at the age of just 16 in August, 2013, pointed a .22 calibre revolver out the window of a friend’s Ford Focus and shot Australian baseball player Chris Lane in the back as he jogged along a street had swirled around the small rural city of Duncan, Oklahoma.

There had been no mention of a motive at Luna’s 3.5 day first-degree murder trial in April when a jury found him guilty and recommended he never be released from jail.

The local police chief, in the days after Lane’s murder, said Luna and two mates, 15-year-old James Edwards and 17-year-old Michael Jones, had confessed to being bored and decided to kill someone.

The “bored” evidence was never mentioned at the trial.

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But there, just as Luna was about to be sentenced on Tuesday, the answer appeared to be etched into his prison jumpsuit.

“I have no doubt he is part of that gang,” Stephens County District Attorney Jason Hicks later told reporters.

Hicks added that Luna, in a pre-sentence report, admitted to being part of the Rollin 90s Crips, a notorious gang founded in Los Angeles’ southern suburbs that had spread across the US.

Hicks said Luna had also been selling drugs before gunning down 22-year-old Lane.

Videos of Luna and Edwards on social media had shown them holding bundles of cash, flashing gang signs and Edwards fooling around with a shot gun.

The murder of Melbourne-raised Lane, who had a baseball sports scholarship with Oklahoma’s East Central University and was visiting his girlfriend Sarah Harper at her family’s home in Duncan, rocked the city.

It caused so much media coverage US President Barack Obama offered his condolences to Lane’s parents.

At the trial the jury heard how Lane decided to go out for a jog and the three boys happened to come across him while in the Ford Focus.

Luna shot him and they sped off in the car, leaving Lane to die.

A 911 call played at the trial gave an horrific window into how the gasping Lane, with a bullet hole in his back, both lungs punctured, two ribs broken and his aorta and pulmonary artery torn, died in agony in a ditch on the side of the road about 10 minutes later.

District Court Judge Ken Graham fought back tears as he spoke of the pain he felt for Lane’s family in Australia and having to sentence a teenager to life behind bars with no chance of parole.

“It’s tough,” the judge said.

“It’s tough on me to sentence a man like that.

“His life is wasted.

“Obviously Christopher Lane’s life is over at no fault of his own.”

Lane’s parents, Peter and Donna, remained in Australia for the sentencing and Harper wasn’t in court, but her parents and family members attended.

Luna’s mother Jennifer said her son was part of a “wannabe gang”, not an actual gang.

She said bonafide gangs were in the neighbouring city of Lawton, but didn’t exist in Duncan.

“That’s all it is – wannabe gangs,” Ms Luna said.

“These little kids running the streets, that’s all it is.”

Luna’s lawyers Jim and Howard Berry filed an appeal minutes after the sentence, arguing the trial should never have been held in close-knit Duncan and that the then 16-year-old should have been prosecuted as a juvenile, not as an adult.

It will take two years for the appeal to be heard.

“We just don’t think we got a fair trial,” Jim Berry said.

Tuesday’s sentence is just another sorry chapter in the Luna’s lives.

Luna’s father, Cornell Dean, is serving a sentence in the Stephens County Jail – his cell located in a different part of the facility.

The teenager’s stepfather died in a motorcycle accident, his brother died from complications of a spider bite and his uncle was killed in a drive-by shooting.

Luna has requested he be moved to one of America’s most notorious prisons – Oklahoma State Penitentiary in McAlester, nicknamed “Big Mac”.

The 107-year-old maximum security prison houses more than 1,100 inmates, is home to the state’s death row and is where executions are undertaken.

Luna couldn’t face a death sentence because he was a juvenile.

Jim Berry said Luna was looking forward to the prison because it has outdoor yards, not like the enclosed Stephens County jail.

Luna’s mother says she has been harassed by locals in Duncan and will move close to McAlester.

When Luna was asked by Judge Graham if he had anything to say before the sentence was announced the teenager shook his head.

Asked later if he thought Luna had shown any remorse the judge had a quick reply.

“Never,” the judge said.

“Never.”