Sierra, a deputy editor and columnist for La Patria newspaper in Manizales, a town in Colombia's coffee-growing region, was shot three times in the head in front of his daughter while walking to work on January 30. He died on February 1.
Sierra wrote a Sunday column for the 80-year-old newspaper in which he frequently highlighted political corruption and human rights abuses committed by leftist guerrillas, a rival right-wing paramilitary army, and state security agents, said Alvaro Segura López, editor of La Patria.
However, the 42-year-old journalist was most critical of local political bosses who, according to a March 6 editorial in El Tiempo, Colombia's top daily newspaper, "run the department like a feudal colony." Sierra frequently accused prominent politicians from the local Liberal and Conservative parties of nepotism, vote buying, and looting public coffers.
Following death threats in 1998, Sierra was assigned bodyguards for a short period but later stopped using them, according to a joint investigation into the journalist's murder carried out by seven of Colombia's leading newspapers and news magazines.
The threats came after regional assemblyman Francisco Ferney Tapasco González was removed from office after authorities discovered that in the 1970s he had been convicted of selling military ration cards while serving as the mayor of Supia, Caldas Department, according to the investigation.
Sierra publicly backed the legal process to remove Tapasco and also used his weekly column to revisit another incident in which the lawmaker was convicted of concealing information about the 1991 murder of a schoolteacher in Caldas, according to the investigation.
Since April 2001, Sierra had also been investigating possible links between Tapasco and a gang of assassins. Shortly before his death he had told colleagues that if anything happened to him Tapasco would be to blame. The former politician denied involvement in the killing.
On the same day Sierra was shot, police arrested 21-year-old Luis Fernando Soto Zapata, who later confessed to having shot Sierra and was sentenced on May 8, 2002, to 19 and a half years in prison.
Soto told the court that he shot Sierra on a whim after mistaking him for a man who allegedly killed a relative several years ago. However, a public prosecutor told CPJ that he doubted the claim, pointing out that footage from a hidden police camera showed Soto lingering for more than two hours before the shooting at the spot where Sierra was killed.
Police also arrested Luis Arley Ortiz on the day Sierra was shot. Authorities released Ortiz soon after, but issued a warrant for his arrest again in May 2, alleging that he acted as a middleman between a gang of assassins and the person or people who allegedly ordered Sierra's death. He was convicted, along with Luis Tabares Hernández, also known as Tilín, to 28 years in prison.
On July 17, authorities charged Francisco Antonio Quintero Tabares with homicide for Sierra's killing. Quintero is believed to be the boss of the gang of hit men that allegedly included Soto.
Fearing the Sierra murder would remain unsolved, seven Colombian newspapers and magazines formed Project Manizales to try to investigate the case. The Sierra killing was also the subject of a documentary, "The Battle of Silence." In the ensuing years, at least nine witnesses were murdered, the Bogotá-based Foundation for Press Freedom (FLIP) said in a statement.
In 2011, nine years after Sierra was killed, authorities arrested Tapasco and charged him with being one of the suspected masterminds of the crime. Tapasco, who has a lengthy criminal record, was also convicted in 2010 for working with paramilitary death squads, according to news reports. In late 2013, Tapasco was acquitted but prosecutors said they would appeal. In June 2015, he was convicted and sentenced to 36 years in prison. The court also convicted Fabio López Escobar and Jorge Hernando López Escobar in the Sierra case and sentenced them to nearly 29 years in prison.
The convictions marked the first time that everyone involved in a journalist's murder had been brought to justice, but as of July 2015, all three men had yet to be apprehended. Tapasco's lawyer said he would appeal his client's conviction to the Supreme Court, according to news reports.