Francis Turatello's assasination had to be the goriest.

On August 17, 1981, during the open yard exercise in the courtyard of Bad'e Carros, the high security prison in Nuoro, Sardinia, Turatello was ambushed by the NCO (Nuova Camorra Organizzata) hitman Pasquale Barra, Vincenzo Andraus and Antonino Faro, two well known assassins from Catania, Sicily. Turatello was unable to escape the ambush.
Barra and Andraus held Turatello, while Faro stabbed him sixty times. In the ensuing confusion from the attack, Andraus was also wounded and would later receive minor surgery in the prison infirmary. After Turatello was dead, Faro disemboweled and chewed Turatello's intestines, then spat it out as a sign of
contempt.

http://en.wikipedia.org/wiki/Francis_Turatello