The mother of a 14-year-old hitman who confessed to severing heads for a brutal Mexican drug cartel pleaded not guilty on Thursday to a charge that she was in the United States illegally, according to news reports. Yolanda Jimenez Lugo, 43, and her husband, Gabriel Aguirre Manuel, 46, pleaded not guilty to charges in federal court in San Diego, the San Diego Union-Tribune newspaper reported.