LOS ANGELES — To many of his neighbors and customers, Lonnie Franklin Jr. was just a friendly mechanic who often stopped to chat as he tinkered on cars in the front driveway of his mint-green house on 81st Street. But after police identified him as a serial killer Wednesday, other neighbors recalled traits that suddenly seemed chilling. Franklin, 57, was charged Wednesday with 10 counts of murder, one count of attempted murder and special circumstance allegations of multiple murders that could make him eligible for the death penalty if convicted.