Local media reported that Marinova had recently been involved in an investigation by a group of Bulgarian journalists into companies involved in EU-funded infrastructure projects administered by local authorities.
Bulgarian interior minister Mladen Marinov insisted on Monday there was no evidence to suggest the killing was linked to Ms Marinova's work.
Bulgaria's prosecutor general, Sotir Tsatsarov, named the suspect as Severin Krasimirov.
The first episode of the show on 30 September broadcast interviews with investigative journalists Dimitar Stoyanov from the Bivol.bg website and Attila Biro from the Romanian Rise Project, about an investigation into alleged fraud involving European Union funds linked to big businessmen and politicians.
In comments carried by the Sofia-based news agency Focus, Marinov said that investigators would now be working to identify any "contacts and problems" she had before the murder.
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Ms Marinova, 30, hosted a show last month featuring two investigative journalists who were detained for their work on suspected fraud involving European Union funds. "Again a courageous journalist falls in the fight for truth and against corruption", the EU Commission's vice president Frans Timmermans tweeted late Sunday.
The German government also condemned the "brutal and terrible murder" of Marinova and said it was imperative that "there is a fast investigation and that this awful event will be illuminated as comprehensively as possible".
Though it wasn't immediately clear whether the killing was connected to Marinova's professional work, her death prompted a concerned response from reporting organizations in Europe. However, Marinova recently interviewed two Romanian journalists who were investigating politicians and businessmen for alleged corruption of European Union funds.
Prime Minister Boyko Borisov expressed hope that the investigation would succeed because of the "work that has been done. None of them true", he told the news conference.
A Bulgarian investigative online site owner has called for an independent worldwide inquiry into the rape and slaying of Bulgarian journalist Viktoria Marinova.
He quoted Juncker as saying previously that "too many" journalists are being intimidated, attacked or murdered and "there is no democracy without a free press".
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The crime has sparked worldwide outcry, with condemnation from the OSCE and the Committee to Protect Journalists.
Ms Marinova is the third European journalist to be killed in the past year. In its 2018 survey, the group described corruption and collusion between media, politicians and oligarchs in Bulgaria as widespread.
"All versions" regarding the murder were on the table, the vice director of local police, Ilian Enchev, said.
Several hundred people, many in tears, attended a vigil in Ruse's central square, lighting candles and laying flowers in front of a portrait of Marinova.
Following Marinova's brutal killing, the Organisation for Security and Co-operation in Europe's representative for media freedom, Harlem Désir, said there was an increasing trend of attacks against female journalists.
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