Bruno Fernandez, 32 an unemployed man from Majadahonda suburb of Madrid was arrested last week over the disappearance of his 55-year-old lodger Adriana Giogiosa.
A search of his house led to the discovery of what was thought to be human remains, including what appeared to be a tooth, on a meatgrinder at the property.
"We can confirm that traces found in the bathtub and in the meatgrinder belonged to that of the Argentinian woman, after DNA testing proved positive," a Civil Guard spokesman told The Local.
Investigators will begin to search a second property on Thursday linked to the suspect who is already in custody.
"A country house In Toledo that belongs to the aunt of the man in custody will be searched today," the Civil Guard spokesman told The Local.
"We still have no trace of where that aunt might be," she added.
The chalet in Majadahonda and the finca in Toledo belong to an aunt of Fernandez who herself has not been seen for years. Fernández claimed that he had "inherited" the property after she was moved to a residential care home. But authorities have no record of her being taken into care.
Investigators had initially been concerned that three other women connected to the alleged killer may also have disappeared.
But they have now discounted them as victims.
"We have managed to locate the three women we were initially concerned about," said the Guardia Civil spokesman.
Neighbours from a former residence of Fernández have described how he regularly sacrificed live animals in apparent satanic rituals, forcing regular complaints to police, according to a report in Tuesday’s El Mundo.