grace rebecca mann , 20 , was found unconscious friday afternoon by two female roommates at their home in fredericksburg , virginia .
the fourth roommate , steven vander briel , 30 , was at home but fled .
he was arrested a few later emerging from woods near church .
briel was charged with first-degree murder and abduction .
mann , a popular junior , reportedly had a plastic bag down her throat .
her father thomas mann is a juvenile and domestic relations court judge in fairfax county .