Zoltan Andrusko, 42, was given a 15-year prison sentence on December 30 and was the only suspect to confess and seek a plea deal to act as a witness in the case.
Prosecutors allege he was the middleman who was tasked with finding the hitmen to kill Kuciak.
The anti-graft reporter and Martina Kusnirova, both 27, were gunned down in their house outside the capital, Bratislava, in February 2018. The double homicide sparked massive protests that led to the resignation of Prime Minister Robert Fico.
Entrepreneur Marian Kocner, about whom Kuciak often reported related to fraud cases involving politically connected businessmen, is accused of contracting the killing.
The court rejected Andrusko’s 10-year plea deal with prosecutors on December 30 and proposed a longer sentence, which he accepted.
“This court considers the extraordinary reduced sentence as justified, as well as logical, but the court, by its decision, should seek justice not only for the accused but for all sides of the case, for society, for justice in the law,” newspaper Dennik N cited judge Pamela Zaleska as saying.
Along with Kocner, the three other defendants — alleged gunmen Tomas Szabo and Miroslav Marcek, and intermediary Alena Zsuzsova — who are all in custody — are scheduled to face trial in the town of Pezinok on January 13.
According to the indictment, Kocner decided “to get rid of Jan Kuciak physically and thus prevent further disclosure of his (Kocner’s) activities” after failing to find “any dirt” to discredit the journalist.
Given that the investigation exposed links between Kocner and police and public officials, the case is seen as a test of Slovak judicial independence.
If convicted, businessman Kocner faces a minimum of 25 years in prison but could be jailed for life.
The killing of Kuciak and Kusnirova stoked public anger over perceived corruption in Slovakia, prompting Fico to step down as prime minister in March 2018.
He was succeeded by environmental activist and lawyer Zuzana Caputova as president in March.