Police investigators said that after "checking the facts" they were unable to bring charges within the legal 48-hour detention period.
The Police said the seven suspects have been released as no evidence was found within 48 hours.
Reporters Without Borders chief Christophe Deloire met with Fico in Bratislava on Friday, days after Slovak investigative journalist Jan Kuciak and his girlfriend Martina Kusnirova were shot dead.
The murders shocked the country and led to protest marches in 25 cities.
Slovak Prime Minister Robert Fico has accused the opposition of using the murder as a "political tool to get people out on the streets and gain power".
The seven suspects were detained during raids in seven locations in eastern Slovakia.
Kanye West's family to play against the Kardashians in 'Celebrity Family Feud'
The only thing that would make this more Kardashian is if Khloe gets paid $5 million to eat the placenta live on Instagram . In 2012, the Mad Men alum claimed that eating her placenta helped to give her more energy when working on set.
The article was published posthumously. One of the men named in Kuciak's report, which probed potential abuse of European Union subsidies and other fraud, had past links to people who subsequently worked for Prime Minister Robert Fico's office.
Slovak media reported that among those held was businessman Antonino Vadala - the owner of several companies - and some of his relatives, alleged by Kuciak to have links to the mafia and contacts in the Slovak government.
Troskova and the secretary of the country's Security Council, also mentioned in Kuciak's reports, resigned on Wednesday pending results of the investigation. In a statement, both denied any involvement in the journalist's killing.
Franco Roberti said on Italian radio: "We warned authorities in Bratislava, but unfortunately they didn't heed us" about the 'Ndrangheta syndicate's expansion into Slovakia.
The rallies are taking place amid calls for global experts to join the investigation and for Interior Minister Robert Kalinak, who was linked to corruption scandals in the past, to resign.
The tensions in Slovakia's coalition government are increasing after the interior minister refused to resign following the slaying of an investigative journalist and his partner.