Mourners are attending candlelit vigils this evening for journalist Viktoria Marinova who was raped and beaten to death in park- as the EU commission urges Bulgaria to find her killer.
Prosecutors said the 30-year-old had been raped, beaten and suffocated with her body left dumped in a park near the Danube river in Ruse on Saturday.
Her mobile phone, car keys, glasses and part of her clothes were missing, detectives said.
Large groups of people have gathered at Liberty Monument in the city of Ruse, Bulgaria, this evening and the capital city of Sofia to pay tribute to the slain journalist who was investigating alleged corruption involving EU funds.
Mourners are holding flowers, candles and pictures of the 30-year-old, as well as images of Anna Politkovskaya, a fearless Russian journalist who was killed in 2006 in her apartment block.
On her last aired TV show, as an anchor, on September 30, Marinova introduced two journalists who were investigating alleged corruption involving EU funds.
She said the regional current affairs show, 'Detector', would do similar investigations.
The European anti-fraud office OLAF declined to comment on the killing, but its press office said it was 'aware of allegations concerning possible misuse of EU funds in Bulgaria that have been brought to light by journalists in recent weeks'.
That appearance was her first time anchoring the show on Ruse-based TV station TVN - a popular channel in northeastern Bulgaria.
Previously, she was best known for presenting a regional lifestyle show and was not a household name nationally.
The European Commission, the European Union's executive said in a tweet today: 'There is no democracy without a free press ... We expect a swift and thorough investigation to bring those responsible to justice.'
Frans Timmermans, commission vice-president, said he was 'shocked by the horrendous murder of Victoria [sic] Marinova'.
He tweeted: 'Again a courageous journalist falls in the fight for truth and against corruption. Those responsible should be brought to justice immediately by the Bulgarian authorities.'
Interior Minister Mladen Marinov said that there was no evidence to suggest a link to Marinova's work as a journalist so far - something echoed by police and prosecutors.
Marinov told reporters on Monday in Ruse, Bulgaria's main river port: 'We are working on all possible motives and we do not exclude any.'
He said no match had been found for DNA samples collected so far from the crime scene, which was close to a psychiatric clinic.
Marinova's final show was a program about Attila Biro, an investigative journalist with the Rise Project Romania and a colleague from the Bulgarian investigative site Bivol.bg, Dimitar Stoyanov.
The two men were briefly detained September 13 south of Sofia, the capital, as they investigated a tip that documents connected to suspected fraud involving EU funds were being shredded and destroyed.
Bivol.bg owner Assen Yordanov said he couldn't directly link Marinova's slaying to her work, but noted her show tackled 'our very sensitive investigation into the misuse of EU funds'.
Police and prosecutors said they were working on three possible motives - whether Marinova was a victim of a random attack by a person with a mental disorder, a planned attack or whether the crime was linked to her personal life.
Chief Prosecutor Sotir Tsatsarov said: 'We do not exclude that it was a random attack, we do not exclude that it was a premeditated attempt on her life.'
Marinova would be the third journalist murdered in the European Union over the past 12 months.
Daphne Caruana Galizia, Malta's best-known investigative reporter, was killed when a bomb blew up her car in October last year and Slovak journalist Jan Kuciak was shot dead with his fiancee at their home in February.
Vigils for Marinova, mother of a seven-year-old daughter, were planned in Ruse and the northern cities of Vidin and Pleven, as well as the capital Sofia.
Prime Minister Boyko Borisov said: 'Thanks to the large amount of DNA material collected it is just a matter of time before the perpetrator will be found.'
The TVN channel expressed shock over the killing of its colleague and board member, but declined to comment further, saying it would give investigators time to do their job first. The channel was due to air a tribute to her later on Monday.
The Organization for Security and Co-operation in Europe's media freedom representative Harlem Desir condemned Marinova's killing on Twitter: 'Shocked by horrific murder of investigative journalist Victoria Marinova in #Bulgaria. Urgently call for a full and thorough investigation. Those responsible must be held to account.'
Reporters Without Borders (RSF) said other TVN journalists should get police protection during the investigation.
The Committee to Protect Journalists said it was 'shocked by the barbaric murder'.
Bulgaria ranked 111 out of 180 countries in the Reporters Without Borders (RSF) world press freedom index this year, lower than any other EU member.
Widespread corruption, shady media ownership and suspected collusion between journalists, politicians, and oligarchs have made objective reporting a constant obstacle course, RSF said.
Reporters Without Borders warned last year about a suspected murder plot against a Bulgarian publisher, Georgi Ezekiev.
Bulgarian journalists at Zov News and the Bivol website were investigating a drug-trafficking ring suspected of having links to police when they uncovered the alleged plan to murder Ezekiev, who publishes Zov News.
One of the reporters involved in the investigation, Maria Dimitrova, received threatening messages by SMS and Facebook.
A journalist is killed on average every week around the world, according to figures compiled by RSF.