A Los Angeles man has been arrested on suspicion of killing a 31-year-old developmentally disabled woman who went missing for six years until her remains were found hidden inside the wall of a Lomita apartment, deputies said Friday.

Randolph Garbutt, 43, lived in the same Harbor Hills Housing Project unit as Raven Joy Campbell, 31, who vanished on June 4, 2009, and whose whereabouts remained a mystery until July 15, 2015, sheriff’s homicide detectives said.

Garbutt was arrested Wednesday on a traffic warrant and immediately booked at the South Los Angeles sheriff’s station on suspicion of murder, sheriff’s Lt. Steve Jauch said.

Held on $1 million bail.

Investigators planned to take their case to the District Attorney’s Office on Monday for seek charges. Garbutt was held on $1 million bail.

Deputies did not say why Garbutt allegedly killed Campbell, who died from blunt force trauma to the head. The weapon used was not located.

Campbell’s older sister, Renee Campbell, said her family was grateful to learn Thursday night of the arrest and thankful for the detectives who solved the case. Family members planned to attend Garbutt’s arraignment Monday in Torrance Superior Court.

Motive unknown

“We don’t really know or understand the motivation and just don’t understand how someone could kill our sister,” Renee Campbell said. “She was very peaceful. She wouldn’t hurt a fly. They wouldn’t have any reason to kill her.”

Raven Campbell lived with her mother in Los Angeles until 2008, when her mother had a stroke. She lived with a brother and at an assisted-living home in Los Angeles until she became distant from family members and moved into a Harbor Hills Housing Project apartment, where a friend, Nicole, lived with her boyfriend.

After Campbell disappeared, Nicole returned her belongings to her family members, saying she had gone shopping and never returned.

Case went cold

Missing persons detectives checked Campbell’s bank and phone records, but came up with nothing. The case went cold.

In 2015, after a story about the missing woman appeared on television, an informant contacted Detective Rich Lopez with information that a body was hidden in the wall of the residence where Raven Campbell had lived on Western Avenue and Palos Verdes Drive North, deputies said.

That weekend, deputies with a cadaver dog checked the apartment. The dog showed interest in a portion of a closet that appeared to have a patched hole. Detectives removed a piece of the patch and noticed something suspicious behind the wall on the floor.

A week later, coroner’s officials and homicide detectives exhumed the human remains from the wall. They were later identified as Campbell.

In August, Campbell’s family cremated her..

‘Healing experience’

“We had a beautiful homecoming celebration for her,” Renee Campbell said. “It was wonderful. It was a really healing experience.”

Homicide detectives were still deep in the investigation Friday and did not reveal details of their case, but Jauch said Garbutt also lived in the apartment with Campbell, and Nicole and her boyfriend.

Why no one knew a body was encased in the wall for so long baffled Campbell’s sister.

“How can you live in an apartment with a decaying body in a wall?” she said. “The stench is not only in her apartment but it’s in the whole area. It’s makes you wonder about the people down there.”

Once Campbell was discovered, the homicide investigation focused on the three roommates. None still lived there when the remains were found.

Couple not involved

Homicide detectives interviewed Nicole and her boyfriend at length, but neither was believed to be involved in Campbell’s death, Jauch said.

Jauch did not reveal how Garbutt was tied to the killing. Garbutt has a criminal record that includes narcotics arrests, he said.

Renee Campbell said, from what she has been told, it appears detectives have a solid case.

“The detectives that were assigned were very diligent,” she said. “We are so gratified about the arrest.”