A 30-year-old man has been detained in Poland in connection with the murder of investigative reporter Peter R. de Vries in Amsterdam last July.

The arrest is the fifth this year in the investigation into the death of De Vries, who was shot dead as he walked from a television studio to his car in Amsterdam. The public prosecution department said it was seeking his extradition.

In July police arrested another Polish man, 27-year-old Krystian M, in what was seen as a breakthrough in the case. He is suspected of having directed the killing and is also said to provide a link to Ridouan Taghi, the alleged gang leader who prosecutors believe ordered De Vries’s assassination.

De Vries had been acting as a confidant to Nabil B, a crown witness in the Marengo case, in which Taghi and 16 other men stand accused of commissioning killings in the Dutch underworld between 2015 and 2017.

Two Dutch men aged 26 and 27, who were arrested in Spain and Curacao respectively in July, are accused of filming the killing and uploading it to social media as a warning to other potential witnesses. Another man, aged 27, was arrested in Helmond, Noord-Brabant, around the same time.

Two other people close to Nabil B., his brother Reduan and his lawyer, Derk Wiersum, have been shot dead in recent years, allegedly on Taghi’s orders.

Delano G, 22, who is accused of shooting De Vries, and Kamil E, 36, who allegedly drove the getaway car, went on trial in June and are currently awaiting the verdict, but they may have to be retried because one of the judges has moved abroad.

E., a Polish national, had moved from his native country to Maurik in Utrecht shortly before the killing. Prosecutors have demanded life sentences for both men.