Bulgarian Interior Minister Mladen Marinov said investigators had found DNA evidence on the clothes and body of Marinova, who was raped and strangled on Saturday in the northern town of Ruse.
Bulgarian authorities were expecting Germany to transfer him to their territory, Marinov said.
Bivol.bg owner Assen Yordanov said he could not directly link Ms Marinova's killing to her work, but noted her 30 September show tackled "our very sensitive investigation into the misuse of European Union funds". 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".
Exposing corruption: Bulgarian TV journalist Viktoria Marinova. He said there was no information that she had been threatened.
"With enormous pain and insurmountable grief the team of TVN television is experiencing the loss of our beloved colleague, Victoria Marinova", TVN said in a statement. "A bow in her memory!"
Journalists' groups and foreign officials expressed shock.
While the reporter did not appear to have been intimately involved in uncovering the alleged fraud, her show touched on a sensitive subject in Bulgaria, where corruption is endemic.
A man detained on Tuesday in Bulgaria was released without charge.
"Her death was caused by blows to the head and suffocation, and her mobile phone, auto keys, glasses and some of her clothing were missing", said Ruse regional prosecutor Georgy Georgiev.
Harlem Desir, media freedom representative for the Organization for Security and Cooperation in Europe's (OSCE) condemned the killing on Twitter, saying that he would closely follow the investigation.
Following the programme hosted by Ms Marinova, Bulgaria's interior ministry said prosecutors were investigating GP Group, a large construction company alleged to have misused the European Union money, and froze €14m in assets.
Marinova is the third journalist to have suffered a violent death in the European Union over the past 12 months, after Jan Kuciak in Slovakia in February and Daphne Caruana Galizia in Malta in October a year ago. They reported that the man left Bulgaria on October 7 for Germany, where his mother lives.