11-year-old charged with first-degree murder in death of 5-year-old brother: DA

CENTENNIAL, Colo. -- An 11-year-old Colorado boy has been charged with first-degree murder after allegedly killing his 5-year-old brother last week, prosecutors said.

The 11-year-old is also charged with an aggravated juvenile offender sentence enhancer, the 18th Judicial District Attorney's Office announced on Tuesday.

The boy was arrested after his 5-year-old brother died on March 10 at a home in Centennial, outside of Denver, according to the Arapahoe County Sheriff's Office.

"It's extremely unusual" for an 11-year-old to be charged with first-degree murder, ABC News legal analyst Brian Buckmire said.

Usually, "someone who is 11 years old doesn't have the mens rea, or the mental capacity, to commit this crime," he said.

Even an 11-year-old testifying in court is rare "because oftentimes we have to go through a hearing to see whether or not an 11-year-old understands the concept of taking an oath," he added.

Details of the alleged crime and the 5-year-old's cause of death were not released; the DA's office said juvenile case records are not public.

"While this minor is being accused of a very serious crime, they are still a child, they are still a minor, and those protections are paramount," Buckmire said.

The sheriff's office said last week that the 11-year-old was in custody at the Marvin W. Foote Youth Services Center.

"Our hearts go out to the family of these two young boys and to everyone in our community who is grieving this loss," Sheriff Tyler Brown said in a statement. "Cases involving the homicide of children are among the most difficult our deputies and investigators face. We know tragedies like this impact not only the family, but also classmates, teachers, and neighbors throughout the community."