Authorities can not yet say whether or not Marinova's murder in the northern Bulgarian city of Ruse was linked to her work as a broadcast journalist, according to Bulgarian Chief Prosecutor Sotir Tsatsarov.
Interior Minister Mladen Marinov said that there was no evidence to link her murder with her work and no information of anyone threatening her, that the case is about "rape and murder".
Chief prosecutor Sotir Tsatsarov said Monday that investigators were considering "all leads" including possible links to Marinova's professional activity.
Some Bulgarian media highlighted the fact that the last broadcast by Marinova involved an interview with Dimitar Stoyanov from the Bivol website and Attila Biro, a Romanian, who received prominent coverage recently when they were arrested while investigating a major company that they allege was involved in abusing European Union funds.
Frans Timmermans, vice president of the EU's executive branch, tweeted: "Again a courageous journalist falls in the fight for truth and against corruption".
"I see deliberate attempts to marginalize this killing and manipulate the public opinion that Viktoria was a victim of a random attack or sexual manslaughter", Assen Yordanov said, adding that Marinova was the only TV journalist who had agreed to host his website's journalists to discuss the investigation.
Working at the private TVN television, she had recently launched a current-events talk show called Detector.
"At this stage let's be careful, not because we don't have anything to say, but because every word uttered loosely could damage our work", he said.
The body of Viktoria Marinova, 30, was discovered in Ruse, northern Bulgaria, on Saturday October 6.
Marinova had been investigating alleged fraud into EU-funded infrastructure projects linked to the authorities and big businesses.
"There is justified worldwide skepticism about the Bulgarian state's commitment to press freedom and only a comprehensive and thorough investigation will assuage those doubts", he added.
Prime Minister Boyko Borisov expressed hope that the investigation would succeed because of the "work that has been done. None of them true", he told a news conference.
He quoted Mr Juncker as saying previously that "too many" journalists are being intimidated, attacked or murdered and "there is no democracy without a free press".
Widespread corruption, shady media ownership and suspected collusion between journalists, politicians, and oligarchs have made objective reporting a constant obstacle course, according to RSF.
Bulgaria is regarded as a laggard in the European Union in terms of press freedom, ranking 111th out of 180 countries, according to Reporters Without Borders (RSF). "It is about rape and murder", he said.
Mourning vigils to honor Marinova are to be held in the capital Sofia and other towns across the country later on Monday.
"In certain countries there is just not enough enforcement of the law", Robert Mahoney, deputy executive director of the Committee to Protect Journalists, told NPR.