A suspect involved in the killing of prominent crime reporter Peter R. de Vries has been arrested by Polish authorities, Dutch prosecutors said on Monday.

De Vries, who campaigned to solve cold cases, was gunned down in Amsterdam in July 2021. He died nine days later from his wounds.

Prosecutors said the 30-year-old Polish man was arrested on suspicion of helping prepare the attack. He is believed to have lived in the Netherlands' second-largest city, Rotterdam, at the time of the shooting.

Dutch authorities have requested that the suspect be transferred to the Netherlands.

What else do we know about the case?

Two men were arrested near The Hague soon after De Vries was shot. Prosecutors in Amsterdam have sought life sentences for both suspects.

One of the two defendants in the murder trial is a Polish citizen.

Another Polish national was arrested in July on suspicion of instructing the two men to kill de Vries. On the same day, two other suspects were arrested in Spain and the Dutch Caribbean territory of Curacao.

Before the shooting, de Vries acted as a confidant for a witness in the trial of members of a crime gang that the police described as an "oiled killing machine." The witness's brother and lawyer were both murdered.

The judiciary believes that the gang is behind de Vries' murder.

sdi/wd (AP, dpa)