Feb. 20, 2009  -- A 9-year-old Arizona boy made up his own mind to plead guilty to a single charge of negligent homicide, the boy's attorney, Ron Wood, said in an interview with ABC's "Good Morning America" today.

The boy had originally entered a plea of not guilty on charges of double homicide for allegedly shooting his father and another man, but the deal allowed him to plead guilty to one count of negligent murder of the other man. The boy's mother was reportedly against the deal and claimed her son was not old enough to understand the agreement.

"He has to make the decision of how he wants to proceed," Wood told "GMA." "As long as we're going to continue to prosecute children, they're going to have to make that decision. ... That's what my young client wanted to do."

According to Wood, Arizona Superior Court Judge Michael Roca determined that the boy was competent to make the decision and his plea was accepted.

The prosecutors decided to drop the charge against the boy for killing his father so he would have a "chance at a normal life," Apache County Attorney Michael Whiting told The Associated Press Thursday.

"How is he going to deal with 'I pleaded guilty to killing my dad?'" Whiting said.

The plea deal allows the boy to undergo psychiatric evaluation with the possibility that he could avoid incarceration.

In the deal with state prosecutors, two charges of premeditated murder in the death of the two men were dropped in exchange for the admission that the boy shot and killed his father's friend.

In return, Whiting wants the boy to undergo extensive mental evaluation and treatment. The plea agreement says any detention will be at the discretion of the court.

The boy will also undergo diagnostic evaluations and mental health examinations at 12, 15 and 17 years old. The reviews are intended partly to determine whether the boy will pose a continuing danger to others.

"There has to be a determination made that there will not be any future danger," the boy's other defense attorney, Benjamin Brewer, told "GMA."

Brewer said the boy would receive education, but if and when he joins other children in a classroom has yet to be determined.

9-Year-Old Upbeat in Plea Hearing

The boy appeared Thursday morning in Apache County Superior Court in St. Johns, Ariz., wearing jeans, a short-sleeve button-down shirt and hiking boots.

Observers in the courtroom described his mood as upbeat as he took a seat next to his mother.

The young shooting suspect had previously pleaded not guilty to the murder charges stemming from the Nov. 5 deaths of his father, Vincent Romero, 29, and Timothy Romans, 39.

The boy could still potentially serve time in a county incarceration facility.

"It's a compromise. No one is really pleased," Brewer told The Associated Press after the hearing.

Whiting said he "had a hard time believing" that the guardian wasn't aware of the plea deal, and the judge accepted the plea despite the mother's concerns.

Police said the boy, who was 8 at the time, used a .22-caliber rifle to shoot the two men. He patiently reloaded the weapon and fired multiple times after they returned home from work.

The boy, whose name has not been released because of his age, confessed during an hour-long interrogation video released by the Arizona's Prosecutor's Office.

In the video, he admitted to the shooting after about 40 minutes of questioning but said it was because his father was already "suffering."

"I went upstairs and then I saw my dad and then I got the gun and then I fired it at my dad," the boy said calmly. "He was on the ground and then I reloaded it."

When police asked whether he shot his father because he was mad at him, the boy offered a noncommittal "hmm" but said he was in trouble "most of the time" at home, mostly for lying.

The police interrogation was conducted without legal counsel present, causing some juvenile defenders to suspect police coercion, which the police have denied.

Police Interviewed the Boy Thinking He Was a Witness

Police said they interviewed the boy because they initially believed he was a witness to the murders, not a suspect.

"I think as the interview progresses there are clearly points where they should have stopped it and gotten him an attorney," Meridith Sopher, supervising attorney at the Legal Aid Society, told "Good Morning America" upon seeing the tape when it was released in December.

The deal may also have been struck because of questions regarding the capacity of a child that young to understand his actions.

"[Kids] are really not as blameworthy," Marcia Levick, director of the Juvenile Law Center at University of Pennsylvania Law School, told "GMA."

"Certainly, their capacity to form that criminal intent and to hold them responsible in the way we blame adults, it doesn't take hold ... until the teen years. I don't think we can make assumptions on whether he was premeditating. He's 8. The question isn't whether we try him as an adult. The question is whether we hold him responsible in the juvenile justice system," she said.

ABC News's Jonann Brady and The Associated Press contributed to this report.