NEW : Jared Loughner 's parents took away his shotgun and told him he needed help . NEW : Loughner bought six or seven boxes of ammunition , documents show . NEW : The FBI has been investigating the shooting for months. NEW : Loughner ran from parents just before the shooting rampage , mom says .
NEW : Jared Loughner 's parents took away his shotgun and told him he needed help . NEW : Loughner bought six or seven boxes of ammunition , documents show . NEW : He purchased a 9mm before Christmas 2010 , investigators say . NEW : Loughner ran from parents just before the shooting rampage , mom says .