“Oak Harbor High School graduate Robert Yates appeared emotional as he pleaded guilty to 13 murders and one attempted murder in Spokane Superior Court on Thursday.In admitting his guilt, the man who locals remember for a strong pitching arm and a polite demeanor takes his place as one of the nation’s most prolific serial killers.But neither Yates nor any of those close to him have given any clues to the motive or the deranged reasoning behind his murder spree.Yates pleaded guilty to avoid the death penalty, though he could still face the ultimate penalty in two Pierce County murders. In pleading, he cleared up the mysteries behind three murders that he wasn’t previously connected to. One of these was in Skagit County, where he dumped the body of Seattle resident Stacy Hawn in 1988.He also pleaded guilty to the two 1975 murders that appear to have been his first, though they don’t follow the pattern of any of the other murders. Yates shot and killed Susan Savage and Patrick Oliver while the two friends were having a Sunday afternoon picnic on Mill Creek, near Walla Walla.The other 10 guilty pleas were for the murders of women in the Spokane area from 1996 to 1998. All of the women were known to have been involved in either drugs or prostitution. Yates picked them up and shot them in the head with a pistol, then dumped them with plastic bags over their heads.A major break in the case came last spring when a woman who survived a brush with Yates came forward. Yates pleaded guilty to attempting to kill her.Ironically, the mother and sister of one of his Yates’ Spokane-area victims lives in Oak Harbor. Debbie Fine and her mother, Margaret Dettman, say that it’s been eerie speaking to many local people who remember Yates from when he lived in Oak Harbor and later in Coupeville.While Yates pleaded guilty to killing 13 people, investigators believe he is responsible for murdering at least three other women. Spokane County prosecutors held back on charging him with the murder of Shawn McClenahan, who was found with another victim in 1997, in case the plea bargain fell through.Yates was scheduled to appear in Pierce County Superior Court next Monday to be arraigned in two other murders, but the hearing was delayed so that Yates can be sentenced in Spokane next Thursday. Prosecutors will ask for the maximum sentence, which could total more than 400 years in prison. “