abdirahman sheik mohamud , 23 , from columbus , said he got training from terror group linked to al qaeda in syria .
was instructed by cleric to return to us and carry out terror attack .
his suspected plan was to go to a military base and kill three-four soldiers ` execution-style '
mohamud was arrested in february on state charges of money laundering and providing support for terrorism .
if convicted in federal case , the 3-year-old could face up to 40 years in prison .