An 11-year-old boy from Colorado in the United States allegedly killed his younger brother while he was napping after school, according to authorities.

Five-year-old Elias Reliford has been identified by his family as the child found dead at his home in the quiet suburb of Centennial, Colorado, on March 10.

The 11-year-old brother has since been charged with first-degree murder in connection with the incident, which occurred one ordinary afternoon after the two children returned home from school, according to their family.

The children's great-aunt, Dawn Myles, revealed that the eldest had been left to do chores while Elias took a nap after school, at the time the tragedy occurred.

"That's when it all happened — while he was sleeping," she said.

The exact details of the circumstances surrounding Elias's death have not been released by the authorities, as the children were minors. The family has also declined to comment further, attempting to cope with this tragic event.

Myles described the murder as "the most horrific act a human being can commit against another, especially a child."

"We never imagined that the big brother he was could hurt Elias," she added on behalf of the devastated parents.

She described the two brothers as inseparable, often playing together and walking around the neighborhood.

"He was very sociable. He loved being outside. Being outdoors was everything to him," she said of Elias, adding that he liked fire trucks and playing pranks.

"If you saw one of the brothers, you saw the other," she added.

Since this tragedy, Elias' family has left their home in Centennial and is now living in hotels while they look for a more stable solution.

The 11-year-old boy is currently being held at the Marvin W. Foote Youth Services Center for minors, according to the Arapahoe County Sheriff's Office.

Myles indicated that she wants Elias to be remembered as a happy kindergarten child, riding his scooter around the neighborhood.