The boy, his grandfather Giuseppe Iannicelli and the grandfather's companion were found dead Jan. 19 in a car in Cosenza.
The attack was related to money, and Iannicelli -- who was under house arrest for a drug conviction -- appeared to be the target of the hit, authorities said.
"In all my years investigating organized crime murders, none has been as horrific as this one," lead prosecutor Franco Giacomantonio told CNN.
Antonia Iannicelli, 24, Coco's mother, is serving a four-year jail sentence for the possession and sale of drugs.
Her two other children, ages 4 and 5, have been moved to protective custody, and she will be allowed to serve the rest of her sentence under house arrest.
The incident has also sparked a debate about how to protect children who grow up in the shadow of their parents' criminal activity.
Interior Minister Alfano Angelino and National Police Chief Alessandro Pansa have signed an emergency protocol in Coco's name to help ensure the protection of children.
"We need ... to make sure the protocol does not forget children who are growing up in vulnerable situations outside the law, who may be victims or witnesses to crimes. We need to make sure Coco is the last child ever killed like this," Pansa said.