PRAGUE (Reuters) - Slovak police detained seven people on Thursday in a probe into the murder of an investigative journalist and his girlfriend, chief of police Tibor Gaspar said.

Participants hold a banner reading: "Attack on journalists = attack on all of us" as they march in honour of murdered Slovak investigative reporter Jan Kuciak and his girlfriend Martina Kusnirova in Bratislava, Slovakia, March 2, 2018. REUTERS/Radovan Stoklasa

The murder of Jan Kuciak, whose reporting focused primarily links between businessmen and top Slovak politicians, was the first of a journalist in the country.

Kuciak and Martina Kusnirova, both 27, were found shot dead in their house north-east of Bratislava last weekend.

The murder prompted demands from Prime Minister Robert Fico’s coalition partners for the resignation of senior officials, throwing the stability of his cabinet into doubt.

Police raided seven locations in eastern Slovakia, Gaspar said on TA3 television. He identified the detainees by their first names and initials and some of these appeared to match names of Italian businesspeople who were the focus of Kuciak’s final report for news website aktuality.sk.

“They have been detained with the prosecutor’s agreement as suspects,” Gaspar said.

Gaspar said in an earlier televised appearance the raids were connected with Italian businessmen who Kuciak alleged in his last article had mafia links. The article was published posthumously.

Gaspar said further proceedings with regard to those detained would be based on evaluation of information gathered.

Gaspar said one of the detainees was Antonino V.

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One of the subjects of Kuciak’s final report was Antonino Vadala, a businessman who the Slovak registry shows briefly owned a firm with Maria Troskova, an aide to Prime Minister Robert Fico.

Reuters was unable to locate Vadala or his legal representatives.

Troskova and the secretary of the country’s Security Council, also mentioned in Kuciak’s reports, resigned on Wednesday pending results of the investigation.

Kuciak’s report did not suggest any wrongdoing by either of the two Fico aides who resigned. In a statement, both denied any involvement in the journalist’s killing.

The case has tapped into a wellspring of public anger over links between Slovak business and politics.

Opposition parties held a protest rally over Kuciak’s killing in Bratislava on Wednesday afternoon and another protest is scheduled in several cities for Friday.

Kuciak also investigated allegations of abuse of EU funds. The European Commission said on Thursday it had requested information from Slovak authorities.

The case raised tension within the ruling three-party coalition.

The junior Most-Hid party said international investigators should be invited to join local police to aid transparency, and also called on Interior Minister Robert Kalinak, a close ally of Fico, whose business acquaintances had been subjects of Kuciak’s earlier articles, to resign.

Party chief Bela Bugar told reporters Most-Hid would leave matters with Fico’s Smer party, and base its next decision on how Smer responded.

Bugar stopped short of threatening to leave the coalition, a step that could force the break-up of the cabinet.

Fico also suffered a blow when, in a related development, Culture Minister Marek Madaric, a long-time senior member of Smer, quit on Wednesday.

Kuciak’s murder was the first of a journalist in Slovakia and the fifth such case concerning a reporter or reporters in the European Union in the past decade, according to Reporters Without Borders (RSF).