A 15-year-old private school class president who is an elite golfer filmed the sexual assault of a 14-year-old schoolmate during a trip to Costa Rica, prosecutors say. 

Vaughn Griffith, who was 14 at the time of the trip, was indicted by a grand jury on January 15 after he was charged as an adult in Las Vegas last year.

He is charged with possessing a visual presentation depicting the sexual conduct of a child, a category B felony punishable by one to six year in prison. 

The private schoolboy from a wealthy family was first taken into juvenile detention on July 29 - eight days after he was named 'Sportsperson of the Year' by the Southern Nevada Junior Golf Association.

Griffith was eighth grade class president at $32,500-a-year The Alexander Dawson School in Summerlin when his class took a trip to Costa Rica last April.

The boys mercilessly bullied a classmate who was on the trip with them, stripping him naked and throwing his clothes on the balcony at Hotel Manuel Antonio, cops said.

Two days later, the boys 'pinned him down and pulled his pants and underwear [down]' on a bed and sexually assaulted him - threatening to cut off his penis if he resisted, according to charging documents. 

Griffith's indictment painfully details the 'graphic and violent sexual assault' as seen in a two minute and 16 seconds video he allegedly posted on Snapchat and saved in his memories.

The teen was shown being held down on the bed and clearly under stress as the boys held him in place.

'The camera angle then reverses back to show Vaughn Griffith and the boys start laughing,' police wrote.

The description of the video alleged the victim yelled as he was repeatedly punched by the other boys, who laughed at his attempts to end their attack. 

He was then allegedly sexually assaulted with a flute, a Chapstick tube, and toothpaste as he cried and screaming in pain and his attackers laughed.

'Victim, because he did not like what was occurring, attempted to get up and leave, but could not get up,' police alleged. 

'Victim stated at this point he saw the group spray sunscreen and toothpaste into his anus, causing it to burn.' 

One boy urged him to fight back, but Griffith allegedly told him that if he did, they would cut off his penis.

The victim eventually managed to free himself and escape, but the boys allegedly continued to mock him.

'Some of the last words heard are one boy stating, "It's clearly sexual", and another boy saying, "Assault",' police wrote.

'The camera angle turns to the person recording, displaying Vaughn Griffith's face.' 

The victim initially kept quiet about the alleged sexual assault because he 'didn't want them to get in trouble'.

He even lied to school staff when he and four other boys were questioned about reports they were spanking each other. They all claimed it was just harmless horseplay and no action was taken.

However, he eventually told his stepmother about the alleged rape, who reported it to school principal Roxanne Stansbury.

Police began investigating in May and later discovered the horrific video of the attack, court documents detailed.

None of the other three boys allegedly involved have been charged as adults and it is unclear if they were charged as minors as juvenile records are sealed.

Whether Vaughn directly participated in the alleged sexual assault is unclear. He is not charged with doing so, only with possessing the video.

Local police in Costa Rica would have to press charges for the assault itself, and this week said they didn't even know about the allegations.

Vaughn was able to be charged because he allegedly still had the video on his phone when it was searched by investigators, police said.

Clark County District Court Judge Linda Marquis ordered in October that he be charged as an adult due to the seriousness of the charges.

His alleged 'possession of a video depicting a horrific group sexual assault of his classmate was heinous and egregious' she wrote in her decision.

Judge Marquis wrote that Griffith 'certainly comes from a supportive family, attended a private school, maintained an excellent GPA, was elected class president, and is an award-winning, elite golfer'.

However, she ruled that had little bearing on the case and a short stay in juvenile detention was inappropriate given the alleged crime.

'The safety of the community requires transfer to the adult system,' she wrote. 

'Certainly there are criminal offenses which are so heinous and so outrageous that standing alone they would require transfer even absent a record of prior criminal activity.'

Judge Marquis overruled Greg Harder, a licensed psychologist, who evaluated Griffith after he was in detention for about a month.

Harder recommended Griffith's case be handled by the juvenile court system and insisted there was no evidence the teen was a sexual predator.

Griffith appeared in court on Thursday after the grand jury indictment was handed down and pleaded not guilty.

He was released on a $20,000 bond posted by his family and ordered to not use the internet except for school, not contact the victim, stay away from minors except his sibling, surrender his passport, and stay out of trouble.

The teen will next face court on June 23 with a trial date set for October.

Griffith's lawyer Joshua Judd said the boy was being treated unfairly by being the only one charged as an adult.

'We are concerned about what is clearly disparate treatment between how Vaughn is being treated compared to other, similarly situated, individuals,' he told 8 News.

'Nonetheless, we look forward to defending Vaughn in this case.'

The Alexander Dawson School's lawyers said it was aware of the 'serious allegations involving male middle school students' during the Costa Rica trip.

'We take any such allegations incredibly seriously and promptly reported them to law enforcement once brought to our attention. 

'Because the alleged misconduct occurred among middle school students, we cannot comment any further at this time.'