An 8-year-old boy faces double-murder charges in the shooting death of his father and another man while residents in the bucolic community of St. Johns try to make sense of the chilling crime.

"This is precedent-setting. We're going to charge an 8-year-old with two counts of homicide," Police Chief Roy Melnick said.

"We haven't had anything like this in Apache County in my 23 years as a prosecutor," County Attorney Criss Candelaria said. "We need to figure out what was going on in this boy's head."

The child's father, 29, and a boarder, Tim Romans, 39, were found dead at the family residence about 5 p.m. Wednesday, shortly after neighbors reported the sound of gunfire. The Arizona Republic is withholding the father's and child's names to avoid identifying a juvenile.

Melnick said police discovered one of the bodies outside the front door, the other in an upstairs room.

St. Johns, the Apache County seat, is a sedate getaway in the high country of eastern Arizona. Its motto: "The Town of Friendly Neighbors." In an online report, the White Mountain Independent newspaper described the slayings as "a shocking tragedy" for the 3,500 residents.

Melnick said the child was near the crime scene when police arrived. The police chief declined to discuss a motive or say how the child came to have a firearm.

Homicides by preteens are extremely rare and present difficult questions for the justice system. Experts say children who kill typically are products of abuse. Once a charge is filed, authorities must deal with issues of culpability, custody and treatment.

The FBI's Uniform Crime Report lists no murder defendants under age 9 since 2005 and only three in the past five years nationally. A search of U.S. news articles uncovered few murder cases involving children as young as the suspect in St. Johns.

In a 1998 case, two Illinois defendants, ages 7 and 8, were accused of killing an 11-year-old but were exonerated. The youngest suspect was a 4-year-old Mississippi girl accused in 2002 of using a brick to kill her brother.

Jeremy Bach, sentenced to 22 years in prison, is among the youngest Maricopa County murder defendants convicted as an adult. At age 13, he shot a friend in 1995.

In 1993, a pair of Chandler girls, ages 11 and 12, were found delinquent in Juvenile Court for killing their adoptive mother.

Melnick said Arizona law generally holds that a child under age 10 lacks competency to be criminally responsible for a homicide.

However, he added, "we think an exception can be made based on the facts and circumstances" in the St. Johns case.

Candelaria said the state will not prosecute the child as an adult. That means the boy would not be sentenced to prison but could remain in juvenile detention until adulthood.

An initial appearance was scheduled Friday afternoon. The outcome was not available late Friday, but Candelaria said the judge likely would require psychological exams to determine competency.

Elaine Newlin, a public defender in Yavapai County who specializes in juvenile cases, said the court also must ascertain whether the boy is capable of understanding proceedings, assisting in his defense and entering a plea.

"I would say offhand that an 8-year-old can't," Newlin added. "This is really an unusual situation."

Although the legal issues are murky, Candelaria said, they are compounded by uncertainty about whether the child should remain in detention, be released to a relative or placed as a state ward.

"Where do we keep him?" he said. "It's obvious there's going to have to be a lot of evaluation."

Melnick said both victims worked at a nearby power plant. The child's stepmother was not home at the time, and there are no other children in the family, he said.