patrick morrison first raped his mentally-disabled niece sabrina morrison in 2007 and after she told a teacher , a rape kit was carried out .
even though the lab found traces of semen , detectives with the maricopa county sheriff 's office closed the case and did not arrest morrison .
he went on to rape his niece for four years and even got her pregnant , although she aborted the child .
the case was re-opened in 2011 and he admitted to the attacks .
it is just one of 400 sex-crime cases that were inadequately investigated by sheriff joe arpaio 's office over a three-year period .