Her body was found dumped near the Danube River in the town of Ruse, northern Bulgaria, on Saturday.
A man has been arrested over the rape and murder of Bulgarian television reporter Viktoria Marinova, who had highlighted possible government corruption, police said.
The Bulgarian government said it had no evidence that Marinova's murder was linked to her work.
"Shocked by the horrendous murder of Victoria Marinova".
Marinova was the host of Defector, a TV news program that launched its first episode on September 30. However, Marinova recently interviewed two Romanian journalists who were investigating politicians and businessmen for alleged corruption of European Union funds.
Krasimirov has been charged with rape and premeditated murder.
"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.
Margaritis Schinas, spokesman for European Commission President Jean-Claude Juncker, said Monday that the commission expected "a swift and thorough investigation. that will bring those responsible to justice and clarify whether this attack was linked to her work".
Prime Minister Boyko Borisov expressed hope that the investigation would succeed because of the "work that has been done".
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He said no match had been found for DNA samples collected so far from the crime scene, which was close to a psychiatric clinic.
This article has been adapted from its original source.
The rape and murder of a Bulgarian journalist who reported on the alleged embezzling of European Union funds has prompted calls for an investigation.
The minister said investigators had spoken to Marinova's family and friends and "there is no apparent link to her work".
United Nations spokesman Stephane Dujarric said Monday that Guterres was "very concerned" about Marinova's slaying and awaited the conclusions of the investigation into her killing. He declined to answer reporters' question about whether there was signs she had been sexually assaulted.
The Committee to Protect Journalists said it was "shocked by the barbaric murder".
Both Ms Caruana Galizia and Mr Kuciak were known for their work exposing corruption, while Ms Marinova's most recent work had been to interview two other Bulgarian journalists, Attila Biro and Dimitar Stoyanov, who were arrested in September while looking into a case of fraud involving the misuse of European Union funds.
Marionva, a former lifestyle journalist, was a television presenter for TVN, a popular channel in northeastern Bulgaria.
The crime has sparked global outcry, with condemnation from the OSCE and the Committee to Protect Journalists.
In what would be her final show to air, Marinova addressed the constraints of practicing journalism in her country. "With tremendous pain and overwhelming grief, the editorial staff is experiencing the loss of our beloved colleague". He accused the mainstream media of leading a "massive smear campaign" against him.