Italian police are looking at the theory that Satanists may have been behind a series of gruesome murders.
Pacciani was dubbed the Monster but died a free man
They believe a cult may have ordered the killing of eight couples between 1968 and 1985 and kept some body parts.
Farm worker Pietro Pacciani, dubbed the Monster of Florence, was convicted of the crimes in 1994 but later released on the basis of flaws in the evidence.
Following new evidence, a pharmacist and three other Florentine professionals are being questioned.
Witness reports of female genitalia and body parts in the fridge of a Tuscan villa linked to a suspected Satanist led police to reopen the case.
The villa had been rented by a doctor thought to have drowned in a lake in 1985 according to Reuters news agency.
The man, who police now think was murdered, is suspected of having been part of a Satanic group who ordered Pacciani and two accomplices to carry out the killings.
"The eight double homicides were carried out according to a criminal plan on two levels," a judicial source told Reuters.
"The execution was entrusted to [Pacciani and his friends] but a group of people who celebrated rituals and black magic put the arms in their hands."
Pacciani died in 1998, two years after his release on appeal and while he was facing a retrial, whilst the two other men were convicted of aiding him
The Guardian newspaper says two previous independent investigations suggested an occult link to the murders.
The victims were shot during romantic trysts in the Tuscan countryside and many suffered sexual mutilations.
Police investigating the 60-year-old pharmacist seized pornographic material from his home.
His lawyer told the Guardian he did not believe his client had anything to do with the killings.
A dermatologist, a businessman and a lawyer from Florence were also being questioned.
The trial of Pacciani, who was given 16 life sentences, was attended by Silence of the Lambs author Thomas Harris who was fascinated by the case.
The fruits of his research in the Chianti region appear in Hannibal, with references to "Il Mostro".
Pacciani died in 1998 at the age of 73 before a retrial.