Menifee, Calif. -

A Menifee teenager pleaded guilty to killing his 11-year-old half-brother, without saying a word as to how or why the crime occurred.

During a juvenile court hearing Friday at the Southwest Justice Center in Murrieta, Skylor Atilano, 17, admitted one count of voluntary manslaughter for the July 6, 2013, death of Terry Dewayne Smith Jr.

Riverside County Superior Court Judge Timothy Freer imposed a 12-year sentence, though under state law, a juvenile convict can only be held until he's 23 years old.  ``It's an end, but a new beginning,'' Shawna Smith, mother of the defendant and victim, told KCAL9 outside the courthouse.

When asked if she had any knowledge of what precipitated the killing, Smith replied, ``I don't think I'll ever know,'' and broke down in tears.  Atilano was arrested after Terry's remains were located behind his family's single-story home in the 33000 block of Helen Lane.

``This was a domestic issue within that residence,'' sheriff's Capt. John Hill said at the time. ``There was no stranger in the city of Menifee who caused this to happen.''

Atilano initially told investigators he had last seen Terry playing video games the night the youngster went missing. But the defendant changed his story soon afterward, indicating he had spotted his sibling walking behind him as he headed to a nearby store, at which point he ordered Terry back home.

The child was reported to be autistic. However, his father, Terry Smith Sr., flatly denied the claim, suggesting that his ex-wife fabricated the disability to obtain state aid.

Terry Jr. had lived with his father in West Virginia until 2009, when the elder Smith suffered a health breakdown and agreed to let Terry come to California to live with his mother, half-brother and sister. 

Terry's death was an emotional blow to the estimated 1,000 volunteers who took part in scouring a 55-square-mile area, looking for the boy.

Volunteers in the predawn hours of July 10 stumbled upon a shallow grave containing partially exposed human remains about 75 feet behind the Smith home and immediately notified deputies. Hill acknowledged that ``multiple searches of the property'' had taken place previously without turning up clues.