PRAGUE (Reuters) - Slovak police are looking into possible foreign links to the murder of an investigative journalist and his girlfriend and are in contact with services in the Czech Republic and Italy, the head of the police said on Tuesday.

A man lights a candle for a tribute to murdered Slovak investigative reporter Jan Kuciak at Slovak National Uprising Square in Bratislava, Slovakia, February 27, 2018. REUTERS/Radovan Stoklasa

The murder of Jan Kuciak, 27, and his fiancée Martina Kusnirova, each killed with a single shot, has shaken Slovakia and led to a wave of anger at perceived high-level corruption in the EU country, the subject of Kuciak’s work.

Police President Tibor Gaspar said on Tuesday that police have questioned around 20 people since Monday and were working on various hypotheses including the possibility that Kuciak was murdered due to his work.

Slovak media reported that among other topics, Kuciak has worked on suspected fraud involving European Union subsidies thought to have been siphoned off to the Italian mafia.

“We have pro-actively communicated first with the Czech Republic - I will not specify the reason exactly - but the case has connection, certain overreach to the Czech Republic,” Gaspar told reporters.

“Naturally we are communicating with Italy, based on all what has been in the media, everyone can make a conclusion why,” he said.

Gaspar said the EU’s police agency Europol has offered expert assistance on issues like analysis of mobile phones.

He said over 20 people have been interrogated and camera footage was being examined.

Gaspar spoke at a joint news conference with Prime Minister Robert Fico, who repeated his call for the public to help with information. He stood next to a table with 1 million euros in cash on it, which the government promised for information that helps solve the case.

Interior Minister Robert Kalinak said a representative of news website aktuality.sk, for whom Kuciak worked, would be invited to join the investigation team to provide maximum transparency.

Kuciak had written articles about tax fraud and businessmen with political connections, including to the ruling Smer party.

The opposition called a protest against corruption and the government for Wednesday afternoon in Bratisalva.