What might have started as horseplay at a Pahrump home ended with a 12-year-old boy dead and his 15-year-old friend charged with murder.

Last week, Anthony Risko was shot in the head by his friend Tyler Aaron Gibbons, authorities said. Gibbons was handling his father's .22-caliber Ruger rifle in his family's home on June 8 -- Risko's 12th birthday -- when he pointed it at the boy's head and pulled the trigger, according to police.

Risko was shot on the right side of the head near the ear, police said.

"It's possible that it started as horseplay and then went too far," said Bob Beckett, Nye County district attorney.

On Saturday, police arrested Gibbons and another teen who was at the house during the shooting, said Nye County Sheriff Tony DeMeo.

Gibbons was booked into the Nye County Detention Center in Pahrump on charges of murder and conspiracy. He is being charged as an adult.

The second teen, who faces conspiracy and obstruction charges, is being treated as a juvenile, DeMeo said.

"My concern is for the family of the victim and the family of the suspect," DeMeo said. "We are saddened by this in the sheriff's office."

Cases involving a juvenile shooting another juvenile are "very rare" in Nye County, he said.

The district attorney's office on Wednesday filed murder charges against Gibbons for the shooting because he showed "an abandoned or malignant heart," Beckett said, referring to a legal term meaning an individual has shown a total disregard for another's safety.

Risko's family referred calls to attorney John Momot, who is representing the family in a possible civil suit against Gibbons. Momot said the family was distraught over the shooting. "It's a rough time," he said.

According to a police report, on the afternoon of June 8, Risko and a 16-year-old were at Gibbons' house, on the west side of Pahrump and north of state Route 372.

Gibbons, the report states, had his father's rifle and pointed it at Risko's head, saying: "This is a real gun ... are you ready .. are you ready?"

Risko was cowering and put his hands up to shield himself, but Gibbons pulled the trigger and shot the 12-year-old, the report states.

Risko was flown to Las Vegas for medical care. He died about 10 p.m. that night at University Medical Center, the Clark County Coroner's office said.

Gibbons and the other teen initially lied to police, saying Risko was handling the weapon when it discharged and the bullet hit him in the head, the report states. The two told police that Gibbons had warned Risko not to play with the rifle because Gibbons' father kept it loaded for security reasons.

But after additional interviews and investigation, authorities concluded that the shooting might have been intentional.

"We don't know what went on in the mind of the shooter, but from his actions and words we can infer intent," Beckett said.

Gibbons' parents have not been charged with any crime, but Beckett said charging them is "something we're looking into."

Last year, a Henderson man was charged with child abuse and neglect in connection with his 12-year-old son's suicide. Authorities said Geoffrey Wells left the shotgun his son had used to kill himself unsecured.

Fred Marik, a friend of Risko's grandmother, said the family had planned to hold a birthday party for Risko on Saturday at a racetrack in Sloan.

"I think anyone with kids knows how horrific this is," Marik said. "I have three kids of my own. I don't know how you cope with that."