WASHINGTON - Police in Slovakia are investigating after Peter Sabo, a reporter for the news outlet Aktuality, found a bullet in his mailbox.

The threat against Sabo comes just over two years after the February 2018 murder of Slovak journalist Jan Kuciak, who worked for the same outlet.

Sabo joined Aktuality a few months after the killing, to help continue Kuciak's investigations. Sabo had recently reported on international tax fraud and drug crimes.  

The outlet condemned the threat in an editorial published in the Slovakian-language outlet on June 26. 

"I would very much like to believe that it was a joke of a child, but after the experience of more than two years ago, I know that if it is not a joke, it can kill," wrote Aktuality editor-in-chief Peter Bardy. "If they think they will intimidate us, they are wrong." 

Police said an investigation is under way, the International Federation of Journalists reported. 

The Slovak Minister of the Interior Roman Mikulec and President of Police Milan Lučansk were informed of the threat, Bardy told the International Press Institute (IPI).  

"This kind of intimidation must be taken seriously," IPI deputy director Scott Griffen said in a statement.  "Threats against Aktuality journalists were not properly investigated in the past, with tragic consequences. Slovak authorities should not make the same mistake again." 

Ricardo Gutierrez, the general secretary of the European Federation of Journalists (EFJ), urged authorities to find those responsible, saying in a statement "Two years after the tragic death of Jan Kuciak, a clear signal must be sent to all Slovak journalists, showing that they can feel safe to do their job."

Before Kuciak was murdered, the journalist had filed a complaint alleging that a businessman, Martin Kočner, had threatened him numerous times. 

Kuciak had been investigating tax fraud of several businessmen who had connections to Slovak politicians and Kočner. 

He was shot dead along with his fiancee, Martina Kusnirova, in their home in Velka Maca, a village east of the Slovak capital Bratislava.

In the weeks after the murder, protests over corruption and the murder led to a series of high-profile resignations including of the prime minister.  

Earlier this year, a court sentenced two people for the murder. Kočner is currently on trial accused of ordering the killing. He denies the charge. 

In a show of solidarity after the murder, Kuciak's colleagues helped finish his unfinished work, and the Organized Crime and Corruption Reporting Project (OCCRP) founded the "Kocner Library" - an electronic archive made up of files police collected in their investigation into the businessman that journalists can use to further report on corruption.