james harris , 30 , got four years and two months in prison in 2011 garroting death of 49-year-old james gerety in kansas .
his ex-girlfriend testified last year that harris kept gerety 's severed head and spoke to it after the slaying .
the woman told the court harris admitted to shooting gerety and torturing him for two days before cutting his head off .
harris originally was charged with first-degree murder but pleaded no contest in december to involuntary manslaughter .
prosecutors said they accepted plea deal because of major problems with evidence and witnesses .