LOS ANGELES -- Robert Durst took the stand at his California murder trial Monday and immediately denied killing his best friend.“Bob, did you kill Susan Berman?” Durst’s attorney Dick DeGuerin said to open the testimony of the 78-year-old New York real estate heir.“No,” Durst answered.“Do you know who did?” DeGuerin asked.“No, I do not,” answered Durst, who sat in a wheelchair instead of the witness chair.Durst was arrested on a warrant in Berman’s killing in New Orleans in 2015 on the eve of