(Providence, RI)--Four people are being charged in federal court in Providence for drug-trafficking and money-laundering conspiracy.The U.S. Justice Department says an operation resulted in at least 50 kilograms of cocaine being trafficked from Puerto Rico to Rhode Island through the U.S. Postal Service, and tens of thousands of dollars in proceeds were allegedly returned to Puerto Rico.Three men - Arcadio Torres of North Providence, Nelson Carvalho of Cranston, and George Mojica of Central Falls -- were ordered detained on Monday, while an arrest warrant was put out for a fourth defendant, not named by the DOJ.