The explosion, which occurred in the town of Pomezia about 20 km (12 miles) south of Rome, destroyed two vehicles belonging to Ranucci, a prominent investigative reporter known for exposing corruption and organized crime. No injuries were reported in the attack.

In a statement, the Carabinieri said the four suspects, detained near Naples, were strongly suspected of possessing, transporting and using explosive devices in a public place, issuing threats and causing damage under aggravating circumstances linked to acting as part of a group using mafia-style methods.

Three of the suspects were placed in pre-trial detention, while a fourth was ordered under house arrest, police said.

Ranucci, host of the investigative television programme “Report” on public broadcaster Rai 3, has lived under police protection for several years because of repeated death threats linked to his reporting.

Speaking to Italy’s ANSA news agency following the bombing, Ranucci said he had received “an endless list of threats.”

The investigation, led by the Rome Anti-Mafia Prosecutor’s Office, involved extensive analysis of surveillance camera footage, telephone records and forensic examinations of the explosive device, according to the Carabinieri.

Investigators believe the individuals who carried out the bombing acted on behalf of unidentified third parties who allegedly organized logistical support, including financial assistance, dedicated mobile phone cards, legal support and contingency plans to facilitate the suspects’ escape abroad if necessary.

Authorities said efforts to identify those believed to have ordered the attack remain ongoing.