单选题 By almost every measure, Paul Pfingst is an unsentimental prosecutor. Last week the San Diego County district attorney said he fully intends to try suspect Charles Andrew Williams, 15, as an adult for the Santana High School shootings. Even before the tragedy, Pfingst had stood behind the controversial California law that mandates treating murder suspects as young as 14 as adults. So nobody would have wagered that Pfingst would also be the first D. A. in the U. S. to launch his very own Innocence Project. Yet last June, Pfingst told his attorneys to go back over old murder and rape convictions and see if any unravel with newly developed DNA-testing tools. In other words, he wanted to revisit past victories — this time playing for the other team. " I think people misunderstand being conservative for being biased," says Pfingst. " I consider myself a pragmatic guy, and I have no interest in putting innocent people in jail. " Around the U. S. , flabbergasted defense attorneys and their jailed clients cheered his move. Among prosecutors, however, there was an awkward pause. After all, each DNA test costs as much as $5, 000. Then there's the unspoken risk: if dozens of innocents turn up, the D. A. will have indicted his shop. But nine months later, no budgets have been busted or prosecutors ousted. Only the rare case merits review. Pfingst's team considers convictions before 1993, when the city started routine DNA testing. They discard cases if the defendant has been released. Of the 560 remaining files, they have re-examined 200, looking for cases with biological evidence and defendants who still claim innocence. They have identified three so far. The most compelling involves a man serving 12 years for molesting a girl who was playing in his apartment. But others were there at the time. Police found a small drop of saliva on the victim's shirt — too small a sample to test in 1991. Today that spot could free a man. Test results are due any day. Inspired by San Diego, 10 other counties in the U. S. are starting DNA audits.