BRATISLAVA (Reuters) - Slovaks returned to the streets in their tens of thousands on Thursday, in one of the biggest demonstrations over the murder of an investigative journalist since protests that forced the prime minister to resign last month.

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The gunning-down of Jan Kuciak, 27, who investigated corruption among politically-connected business people, and his fiancee at their home in February increased widespread anger about persistent corruption allegations.

Long-serving prime minister Robert Fico stepped down to save his three-party government, and picked his deputy, Peter Pellegrini, to lead a reshuffled cabinet.

Thursday’s protesters - estimated to number up to 45,000 by News website Dennik N, close to the 50,000 who marched at the height of protests last month - demanded more tangible change and called for the police chief to resign. Police did not provide any crowd figures.

“The new government hasn’t done anything to convince me it will be different than the old government,” 38-year-old protester Jan Filip said.

“Almost all of the cases Kuciak covered could already have been investigated, yet none of them made it to court.”

Protester’s said police chief Tibor Gaspar must go, and called for the law to be changed to prevent the interior minister naming his successor, something they said might ensure an impartial investigation of Kuciak’s murder.

President Andrej Kiska repeated his calls for Gaspar to resign to help rebuild public trust.

Interior Minister Tomas Drucker said he may need weeks to assess Gaspar’s performance.

Kuciak, who police believe was murdered in a contract killing related to his journalism, used to report on suspected tax fraud, sometimes by people with links to the ruling Smer party.

He also reported on deals between the government and the country’s biggest privately-owned security firm, whose owner is related to Gaspar. The police chief has denied any wrongdoing.

Gaspar was appointed in 2012 by Robert Kalinak, who resigned as interior minister last month. Kuciak had published stories about Kalinak, who has denied wrongdoing.

Before his death, Kuciak was investigating Italian businessmen in Slovakia with suspected mafia links, one of whom had had business dealings with two people who later worked in Fico’s office before resigning in the wake of the murder.

The two have denied any links to the killing.

According to Transparency International, no senior Slovak politician has been sent to prison for corruption in the past six years, while six regional politicians have been given suspended sentences. About 48 percent of bribe cases dealt with by courts involved amounts of less than 100 euros.