Now Corinne Vella, sister of murdered Maltese journalist Daphne Caruana Galizia, has told Euronews countries need to work together.
The editor and co-founder of the Organized Crime and Corruption Reporting Project, OCCRP, Drew Sullivan, also demanded an independent investigation.
Bulgarian Interior Minister Mladen Marinov insisted Monday there was no evidence to suggest the killing was linked to Marinova's work.
Bulgaria's top prosecutor says authorities have no new leads on the motives for the rape and slaying of a Bulgarian television reporter.
Marinov said investigators are now working to identify any "contacts and problems" she had before the murder.
"It's unsafe to be a journalist in Bulgaria and physical assault is just one of the threats", says Silvia Velikova, a senior journalist from Bulgarian National Radio who covers the judiciary and politics.More news: Senate confirms Kavanaugh to high court
In the Bulgarian capital of Sofia, mourners gathered outside a church.
"Viktoria's death, the brutal manner in which she was killed, is an execution", Yordanov said.
In another high-profile case, journalist Dilyana Gaytandzhieva broke news past year that large caches of U.S., Saudi, and Bulgarian weapons were secretly being shipped to Syria.
The killing turns the spotlight not only on Bulgaria - which is ranked 111th in the world for press freedom, the lowest of any European Union state - but also non-EU states including Ukraine Kosovo, Montenegro and Serbia.
Police investigators walk near a crime scene where TV journalist Viktoria Marinova was murdered in Ruse, Bulgaria on October 7, 2018.
The pair were briefly detained by police, drawing condemnation from Reporters Without Borders (RSF). "Investigative journalists are being systematically removed", Marinova said in her conclusion on the last Detector episode, aired on 30 September, adding that her show would give a forum to investigative journalists and engage in its own investigations in future.More news: Microsoft announces its take on game streaming: Project xCloud
EURACTIV has reported about this corruption case in November 2015.
The Committee to Protect Journalists called on Bulgarian authorities to conduct a "rigorous, thorough investigation" into the killing.
He quoted Juncker as saying previously that "too many" journalists were being intimidated, attacked or murdered and "there is no democracy without a free press".
Giegold said, "First Malta, then Slovakia, now Bulgaria".
"The country has a bad image with regard to press freedom, but it's possible that there is no link to this case", said Svetoslav Terziev, opposition media analyst who also teaches journalism.
The Bulgaria-based Association of European Journalists said reporters from small regional and local media are under particular pressure and even face threats from local businessmen and politicians, often leading to self-censorship.More news: Fox hires ex-Trump aide Hope Hicks