The Guardian's Ed Pilkington interviews Quantel Lotts, now 26 years old. guardian.co.uk

When Quantel Lotts was 17 he put together a makeshift tattoo gun using the motor of an old Walkman casette player and a stylus fashioned from a sharpened staple. Then he asked a fellow inmate to etch two words in Gothic script down each of his outer forearms.

On his right arm he wrote DEAD. On his left arm he wrote MAN.

"That's how I felt at the time, like I was already dead," he says.

He had just been handed down the most severe punishment – short of execution – possible in America. He was tried as an adult for a homicide he committed when he was 14 years and 21 days old, and sentenced to life without parole. He will remain in jail until he dies.

Now 26, Lott has seen his tattoos blur slightly, but his punishment remains as sharp as the moment the jury pronounced him guilty. Under the terms of his sentence, he will never stand before a parole board, never have the chance to reveal how much he's changed, never be able to show that the impulsive kid who killed his step-brother in an adolescent fight 12 years ago no longer exists.

He will never be free.

"They locked me up and gave me life without. It's like they killed all hope for the future. There's nothing left."

Quantel Lotts does have one last hope. On Tuesday the US supreme court, the highest judicial panel in the land, will consider whether children should be sentenced to die in prison for homicides committed when they were 13 and 14.

The nine justices of the court will deliberate on the test case of Kuntrell Jackson from Arkansas, who was 14 in 1999 when he and two older boys tried to rob a video store. Jackson stood outside the shop while the other two went in and shot to death the storekeeper, and though he was not even in the room, he was still tried as an adult and sentenced to life without parole.

The judges will also consider the case of Evan Miller from Alabama, sentenced to die in prison for a 2003 homicide that happened when he was also 14. He and an older youth beat a 52-year-old man, then set fire to his home, leading to the man's death from smoke inhalation.

At the oral argument, the lawyer for Jackson and Miller, Bryan Stevenson of the Equal Justice Initiative, will say that life without parole for such young kids is a violation of the eighth amendment of the US constitution that prohibits "cruel and unusual punishment". He will also argue that such sentences fly in the face of modern understanding of adolescence – the changing nature of the brain, the social pressures on teenagers, the change inherent in their transition from childhood to adulthood.

In recent years the supreme court has been gradually whittling away the harshest sentences for kids. In 2005 it ruled that it was unconstitutional to impose the death penalty for crimes committed under the age of 18, and two years ago the court ruled that juveniles who commit crimes in which nobody is killed cannot be given life without parole.

But that still leaves about 2,500 people in America sentenced to die in prison having been 17 or younger when they committed their crime. Within that group, 79 prisoners were, like Quantel Lotts, just 13 and 14 years old at the time.

There is a singularly brutal quality to this aspect of US justice. America is the only country in the world, bar none, that is known to sentence children to die in prison without any hope of release. Even in a country that practices the death penalty it has the ability to shock, because this is a living death.

"All I want is another chance," says Lotts. "A shot at living an actual life. I've been in prison since I was 14, so I don't know too much about anything – I've never been anywhere, done anything. I've never lived a life."

A troubled childhood, no future

Lotts grew up in St Louis, Missouri, in a classically disturbed family. His mother, father, step-mother, uncles and aunts were all on crack cocaine, regularly getting high on the drug in his presence.

Violence was as ordinary in the family as milk. When Lotts was 11 he saw his uncle get shot five times in a drug dispute. He himself was regularly beaten – with brooms and shoes, belts and extension cords, curtain balls and Wiffle bats. As a child he was taught to settle disputes with the fist.

"I was taught that most problems can be solved with violence. When I was little they used to put socks over our hands and make us fight each other – that's how it goes, that's all I knew."

Quantel Lotts around the time of the killing.

By the age of 14, Lotts had regular outbursts of anger followed by uncontrollable crying and amnesia about what had happened. Despite such volatile behaviour, he received no medical or therapeutic help.

In November 1999 he was play-fighting with his step-brother Michael. First Michael hit him with a blow dart, then Lotts responded with a toy bow and arrow. It escalated into a fight, and Lotts stabbed Michael once or twice with a knife, killing him.

He has no recollection of the incident, though he does remember being told later that day what had happened. "I was crushed. I just cried and cried and cried. My brother was dead and they said that I did it. That just killed me."

In the early years of his incarceration, Lotts says that he had frequent moments of despair and tried to commit suicide three times. "I was tired of being in prison. From 14 to 18 was an incredibly long time for me, I couldn't foresee myself spending the rest of my life like that."

But as time passed he found himself changing. The 14-year-old Quantel Lotts – impulsive, volatile, angry, violent – began to fade away.

"I had to grow up fast in prison. The biggest change is that I've learnt to control my temper. The older I got I didn't get as mad anymore, it's like I grew out of it," he says.

Lotts sees himself now as a completely different person to the boy who killed his step-brother. But his sentence makes no account for that.

The state of Missouri considers the age at which he killed his step-brother – 14 – as too young legally to be allowed to sell fireworks, donate blood, leave school, have a tattoo without parental approval, get married, consent to sex, work unlimited hours, be licensed as a barber, work as a cosmetologist or manicurist, or enter a contract. It was not too young, by state law, to be tried as an adult and sentenced to remain incarcerated forever.

Lotts says he tries not to think about it. "It's hard. I can't accept that I'll be here for the rest of my life. They might as well have given me the death penalty, it's just the same."

He also tries not to think about tomorrow's supreme court session and its eventual ruling, expected sometime this summer. "I don't like to get too far involved with it, because if I get my hopes up too high and it doesn't happen, I'm not sure I can handle the crash."

Overall, he's doing much better than he used to, largely because he's developed coping mechanisms to deal with despair. He calms himself when he feels agitated by listening to music – Jagged Edge, Christina Aguilera and the aptly-named Boyz II Men. He speaks by phone all the time to his wife Ingrid, who he married last year having got to know her as a pen pal.

And he regularly goes to prison chapel, where he contemplates the meaning of redemption. He thinks about that a lot. On the inside of his right forearm he bears another tattoo, etched into his skin by sharpened staple. It says: "UNFORGIVEN".