Three cats have been found dead over the past few days in the historic Sant'Anna area of the island, Il Mattino reported.
The deaths follow a spate of poisonings over the summer, which sparked outrage and protests across the island.
Posters with the slogan, "Shame on you. We hope you're next, suffering the same agony", appeared on the island's streets in August.
Animal-rights group, "I Migliori Amici" ("Best Friends") filed a complaint with the authorities demanding they investigate.