A popular Bulgarian TV journalist was found raped and murdered in a case that has shocked Europe.
The body of Viktoria Marinova was discovered in a park near the Danube River in Ruse on Saturday.
The 30-year-old had been raped, beaten and suffocated, prosecutors said.
The European Commission has now urged Bulgaria to conduct a rapid investigation into the murder as hundreds of mourners held vigils across the country.
"There is no democracy without a free press ... We expect a swift and thorough investigation to bring those responsible to justice," the European Union's executive said in a tweet.
Bulgaria ranked 111 out of 180 countries in the Reporters Without Borders world press freedom index this year, lower than any other EU member.
While there has been no link established to her work so far, the killing has angered and upset many in a country where people are frustrated with rampant corruption and an inefficient and graft-prone judiciary, for which Sofia has been repeatedly rapped by the European Commission.
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".
Marinova's appearance on "Detector" was the first time she had anchored 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.
Interior Minister Mladen Marinov has said that there was no evidence to suggest a link to Marinova's work as journalist so far - something echoed by police and prosecutors.
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"We are working on all possible motives and we do not exclude any," Marinov told reporters on Monday in Ruse, Bulgaria's main Danube river port city.
He said no match had been found so far for DNA collected from the crime scene, which was close to a psychiatric clinic.
Hundreds of people flocked to Ruse's main square to put flowers in front of a picture of Marinova, with some in the crowds urging the authorities not to play down the possibility her work was a reason for the killing.
"I strongly hope that the truth will soon be uncovered, her perpetrator or perpetrators found and justly punished," Teodora Shopova said after lighting a candle at the vigil.
Vigils for Marinova, mother of a seven-year-old daughter, were also held in downtown Sofia as well as several other cities, with many demanding justice and an independent, even international, investigation.
The TVN channel expressed shock over the killing of its colleague and board member, but declined to comment further.