Several hundred people, many in tears, attended a vigil in Ruse's central square, lighting candles and laying flowers in front of a portrait of Marinova. A similar observance was held in Sofia.

In Ruse, many told AFP they had known Marinova personally as she had been active with charities in the town on the Danube.

Chief prosecutor Sotir Tsatsarov said Monday that investigators were considering "all leads" including possible links to Marinova's professional activity.

Authorities in Bulgaria, the EU's poorest member state plagued by rampant corruption, earlier revealed that Marinova had been killed by blows to the head and from suffocation, and had also been raped.

"We are in shock. In no way, under any form, never have we received any threats -- aimed at her or the television," a journalist from Marinova's own TVN told AFP on condition of anonymity Sunday, adding that he and his colleagues feared for their safety.

UNESCO chief Audrey Azoulay condemned the murder, saying: “The use of sexual and physical abuse to silence a woman journalist is an outrage against the dignity and basic human rights of every woman."

In a statement from the UN cultural agency's headquarters in Paris, Azoulay added: "Attacks on journalists erode the fundamental human right to freedom of expression and its corollaries, press freedom and free access to information."

Marinova is the third journalist to be murdered in Europe in the past 12 months after Jan Kuciak in Slovakia in February and Daphne Caruana Galizia in Malta in October 2017.

Bulgaria is regarded as a laggard in the EU in matters of press freedom, ranking 111th out of a total 180 in this area, according to Reporters Without Borders (RSF).

"Shocked by the horrendous murder of Victoria Marinova. Again a courageous journalist falls in the fight for truth and against corruption," the EU Commission's vice president Frans Timmermans tweeted late Sunday.

- 'A warning'? -

Condolences poured in on social media for Marinova, who leaves behind a small child.

Some observers believe the murder could be linked to Marinova's work.

The first episode of her programme, aired on September 30, featured an investigation into fraud allegations against oligarchs and politicians.

She interviewed the reporters behind the probe, investigative journalists Dimitar Stoyanov from the Bivol.bg website and Attila Biro from the Romanian Rise Project.

Bivol.bg owner Asen Yordanov told AFP that "Viktoria's death, the brutal manner in which she was killed, is an execution. It was meant to serve as an example, something like a warning."

The crime has sparked international outcry, with condemnation from the OSCE and the Committee to Protect Journalists.

In Bulgaria, however, national TV networks gave scant air time to the case.

And even some of Marinova's fellow journalists were not convinced that she was killed because of her reporting.

"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 and journalism teacher.

At the Ruse vigil, telecoms technician Venelin Rumenov, 27, told AFP: "I don't think that she had been threatened or anything."

- Reporting obstacles -

Widespread corruption, shady media ownership and suspected collusion between journalists, politicians and oligarchs have made objective reporting a constant obstacle course, according to RSF.

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.

Violence against women has also been widespread in Bulgaria.

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