The four include the alleged mastermind, a businessman who was long suspected of involvement in the crime. The prosecutors previously identified him as Marian K., omitting his full last name as is standard in Slovakia.
Reporter Jan Kuciak and his fiancee Martina Kusnirova were fatally shot in their home on Feb. 21, 2018. Slovak authorities believe it was a contract killing linked to Kuciak's work investigating possible government corruption.
The killings triggered major street protests and a political crisis that led to the dismissal of the national police chief and the government's collapse.
The prosecutors previously said 70,000 euros ($78,000) was paid for the alleged contract slayings.
Copyright 2019 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.