More people may face charges for the murder of a Slovak investigative journalist, the country's top prosecutor said on Monday, after police made their first arrests for the killing that rattled the nation and toppled its government.

The killing of Jan Kuciak, 27, and his fiancée at their home outside the capital Bratislava in February stoked public anger over corruption and prompted the largest protests in Slovakia since the end of Communist rule in 1989.

Kuciak probed fraud involving businessmen with Slovak political ties and had worked on a story about suspected Mafia links of Italians working in Slovakia.

Police carried out raids last week and a court on Sunday ordered four people jailed until trial for the murders.

"We have more steps prepared which we want to take, so there is high probability there will be more charges," Slovak general prosecutor Jaromir Ciznar told a news conference.

"We're still in the stage where charges have been pressed and we should not be too optimistic but the evidence is very strong," he added.

We have more steps prepared which we want to take, so there is high probability there will be more charges

Prosecutors said the killer was paid €70,000, of which €50,000 was cash and the rest forgiven debt.

Police arrested a woman on Friday identified as A.Z. and said she had likely paid the money to the killers but the motive and whether she worked for someone else was unclear.

A police investigator told a briefing that weapons, cars, a cell phone used during the crime, and a bullet corresponding to the cartridge case found at the crime scene were seized in home searches last week.

Police chief Milan Lucansky said the suspected killer was a former police officer.

In his final story, published posthumously, Kuciak reported on an Italian living in Slovakia with past business links to two Slovaks who later worked in then-prime minister Robert Fico's office.

Both of the Slovaks resigned but deny connections to the murder. Their Italian former business partner has also denied connections with the mafia and the murder but was detained on a European drug trafficking warrant in March and extradited to Italy in May.

Weeks of protests that drew tens of thousands in March forced the departure of long-serving leader Fico as well as the interior minister and police chief but the coalition government remains in power.