High school freshman Charles Andrew Williams, 15, was taken into custody Monday after he allegedly opened fire on his San Diego, Calif., campus, killing two fellow students (ages 14 and 17) and wounding 13 other people, according to authorities. The incident, which is sparking comment nationwide, is being called the worst episode of school violence since 1999's shootings at Columbine High school in Littleton, Colo. Witnesses say that Williams, described by The New York Times as slight and baby-faced, smiled as he pulled the trigger on what authorities said was a .22-caliber pistol. He reportedly surrendered on his knees in a school bathroom with the declaration, "It's only me." Fellow students at Santana High told reporters that Williams's threats about taking a gun to campus were not taken seriously. Under California law, Williams will be tried as an adult. He is expected to be arraigned on Wednesday on charges of murder, assault and weapons possession.