Federal authorities have arrested a man accused of plotting a terrorist attack at Mall of America and pledging his allegiance to the Islamic State group. According to an affidavit unsealed on Wednesday, FBI agents arrested 18-year-old Sheikhdoon Abdullahi Mohamud on Tuesday directly after he purchased an AK-47 and 200 rounds of ammunition with the stated intent of carrying out a mass shooting. The criminal complaint alleges Mohamud had messaged an informant for nearly two years, discussing his hatred of non-Muslims and his desire to align with an Islamic terror group. He floated the idea of joining al Qaeda and al...