A detective reportedly told the Los Angeles Times on Monday that ''it doesn't look very good that [Sandra Rosas] is alive.'' He added that investigators believe her half-brother Gabriel Gomez, 39, ''is the party responsible.''

Gomez was arrested for suspicion of kidnapping on Oct. 24, but the District Attorney's office decided against immediately filing charges against him. He remains jailed, however, on an unrelated parole violation. Detectives, who reportedly have been building a case against Gomez, could turn the case over to the DA's office for prosecution as early as this week, according to the Times report.

Gomez and Sandra Rosas reportedly first met about five years ago, and relatives told police that she went out of her way to help her half-brother, even allowing him to live on the family's property for a time.

Sandra Rosas was last seen by her daughters at the Rosas' Rowland Heights home at 8:30 p.m. on Oct 23. When they returned to the house at about 11 p.m., their mother and the family's van were gone. Shattered glass was found in the driveway, and the door to the home was left wide open, the daughters told authorities.

After discovering that their mother was gone, one of Rosas' daughters called her mother's cell phone. When the cell phone activated, the daughter heard Gomez on the line ''making threats regarding [her] mother's life,'' the detective reportedly told the Times.

Authorities later found the van in the nearby city of La Puente, and found blood inside.

Cesar Rosas was on the road with Los Lobos in Louisiana when he received word of his wife's disappearance, whereupon he returned home. He told members of the press that he last spoke with her at 7 p.m. on Oct. 23. Later that night, the band took the stage at the House of Blues in New Orleans.

Los Lobos performed without him at The Grant Street Dancehall in Lafayette on Sunday (10/24). The band has not played a concert since.

Los Lobos was touring in support of their recently released album ''This Time'' (Hollywood).