By TEDD THOMEV *(Independent St*ff Writer)nn ANA—Shaking with fear, Billy Rupp, 18, cowerelt;on a chan in Orange County Justice Court here yesterday after noon and heard himself charged with the brutal first-degrelt;sex-murder of a pretty Yorba Linda baby-sitter.Shortly afterward, Dist. Atty-----James L. Davis announced* that hewill seek the death penalty for Rupp,The court hearing came only a few hours after the disheveledyouth—a five day growth of blondish whiskers covering his chin—had confessed to authorities that an uncontrollable sex urcehad driven him to kill Ruby Ann Payne, 15, last Friday.“I had to kill her,” he mumbled. I had my eye on her a long time. I meant to rape her.Handcuffed to sheriff’s aides, Rupp was led at 1:45 p. m. from the Orange County jail to theSee RUPP, Page 0-AA WALK IN THE SUN—Handcuffed to Undersheriff Steve DuHart, Billy Rupp. 18. walks from the Orange County Jail m tsanta Ana to his arraignment yesterday in the Justice Court, a block away. Earlier, the youth confessed the sex slaying of a pretty Yorba Linda baby-sitter. More pictures onPage 3-A. (Independent PKoto kg John M H eagle)