The two were detained as part of the investigation of the person or persons who ordered the murder of De Vries, who was shot at close range on a busy street in Amsterdam on July 6 last year. The campaign journalist died nine days later at the age of 64.
The prosecutor gave no details about the identity of the new suspects or their alleged roles in the killing.
On Monday, the prosecution announced that they had arrested a 27-year-old Polish man suspected of organizing the hit.
Two other suspects – the alleged gunman and fugitive driver – have been prosecuted in Amsterdam on a charge of murder. The judges are due to deliver their verdicts on July 14. Prosecutors sought life sentences for both men.
De Vries made his name as a crime journalist. Later in his career, he tirelessly campaigned to resolve cold issues. Prior to his shooting, De Vries had been an adviser and confidant to a witness in the trial against the alleged leader and other members of a criminal gang, which police described as an “oiled killing machine.” The witness’ brother and his lawyer were both murdered.
Prosecutors last month called on the judges to convict the suspected gang leader, Ridouan Taghi, of several murders and sentence him to life in prison. Judgments are expected in his trial next year. Taghi has not been charged with the murder of De Vries.