The European Commission has urged Bulgaria to conduct a rapid investigation into the killing of TV journalist Viktoria Marinova as mourners planned vigils near her home town.
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.
On her last aired TV show, as an anchor, on September 30, Marinova introduced two journalists who were investigating alleged corruption involving EU funds.
Police sources said that the crime did not immediately appear linked to Ms Marinova's work
Television journalist, Viktoria Marinova, was brutally murdered in Bulgaria's northern town of Ruse
Police walk near a crime scene in Ruse. Investigators ate looking into whether the killing was motivated by her work, personal life or was committed by a random attacker
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.'
The 30-year-old was raped, beaten and suffocated before her body left dumped in a park near the Danube river
Marinova's last news broadcast was on TV station TVN - a popular channel in northeastern Bulgaria - and was about an investigation into alleged misuse of EU funds
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.
Ms Marinova would be the third journalist murdered in the European Union over the past 12 months
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'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