The president of two San Diego-based Somalian organizations pleaded not guilty yesterday to lying about taking money from a group linked to terrorists. Community leaders and his family said they were mystified by the charges. Omar Abdi Mohammed, 41, a teacher's assistant in a San Diego elementary school, was described by prosecutors in federal court as a shadowy figure who collected more than $351,000 from a group accused of financing international terrorism. Prosecutors have refused to say what they believe Mohammed did with the money, but they said in court that, in addition to the $351,000, he also received $1,700...