Medina, 53, was returning from a reporting trip outside the eastern city of Curuguaty when his vehicle was intercepted by two camouflage-clad gunmen on a motorcycle, Néstor Cañete, the public prosecutor investigating the case, told reporters.
Cañete said Medina was shot four times in the face and chest with a 9mm pistol and died at the wheel of his vehicle. Antonia Maribel Almada, 19, who was Medina's assistant and was in the vehicle, was also killed in the attack near the village of Villa Ygatimí, according to news reports.
On the day of the attack, Medina, a regional correspondent for Paraguay's largest independent newspaper, ABC Color, was covering a story about the alleged use of toxic pesticides on farmland, according to news reports.
Interior Minister Francisco de Vargas told reporters the murder was related to Medina's coverage of the booming marijuana trade in Canindeyú department, which borders Brazil and is a major drug trafficking route. Canindeyú has also been the site of violent land disputes, according to news reports.
"Pablo Medina was the object of many threats mainly due to his journalistic investigations of marijuana production," Vargas told reporters.
Vargas said police had been providing Medina with bodyguards, but the journalist was unescorted at the time of the attack. Some media reports said Medina occasionally went out without the protection if guards were unavailable.
In 2001, Medina's brother, radio journalist Salvador Medina Velázquez, was killed after denouncing political corruption. His death prompted Pablo Medina, who was already working for ABC Color, to temporarily flee Canindeyú department.
Nelson Zapata, who was Pablo Medina's editor at ABC Color for many years, told a local radio station that Medina had been receiving threats "almost since he started out in journalism."
In the days after the murder, authorities charged Vilmar "Neneco" Acosta Marques, mayor of Ypejhú, a city about 90 kilometers from Curuguaty and which borders Brazil, with ordering the murder. Authorities raided Acosta's property and found weapons, large amounts of marijuana, and tools used to produce marijuana, according to news reports. ABC Color reported that Acosta, who fled the town, was heavily involved in drug trafficking and that he and other drug traffickers were angered by Medina's coverage of the marijuana trade because it had disrupted their business.
The mayor's brother, Wilson Acosta Marques, cousin Flavio Acosta Riveros, and driver, Arnaldo Javier Cabrera López, were also charged with being the gunmen and accomplices. All the men were fugitives and Acosta was replaced as mayor, according to news reports.
According to news reports, records showed that nearly two weeks after the murder, Acosta crossed the border to renew his driving permit in Brazil, where he has dual citizenship. The reports said authorities feared that Acosta had fled to Brazil because the country does not have an extradition treaty with Paraguay. Authorities requested an international warrant for the arrest of all four men from Interpol, according to news reports.
ABC Color alleged that Acosta's political and police connections, including a prominent congresswoman, had allowed the men to flee. Public prosecutor Cañete was later removed from the investigation for allegedly having intervened on Acosta's behalf in previous criminal cases, according to news reports. On November 8, 2014, authorities arrested an individual they accused of belonging to Acosta's criminal group and helping him escape.
Three weeks after the murder, the Paraguayan congress announced the creation of a bicameral commission to investigate the crime, according to news reports.