A 30-year-old man suspected of being involved in the murder of crime reporter Peter R. de Vries has been arrested in Poland, Dutch prosecutors said.

Mr de Vries, one of the Netherlands’ best-known journalists who campaigned to solve cold cases, was shot in Amsterdam last July 6.

He died of his injuries nine days later aged 64.

The Pole is being held on suspicion of helping to prepare the attack and is believed to have lived in the Dutch port city of Rotterdam at the time of the shooting, prosectors said on Monday.

His identity has not been released in line with local privacy regulations.

Dutch authorities have asked for him to be moved to the Netherlands.

Two men were arrested near The Hague soon after Mr de Vries were shot and are on trial for his murder.

Prosecutors want life sentences.

One of them is a Polish national, Kamil E, who is the alleged getaway driver.

Another Pole was arrested in July on suspicion of instructing the two men who carried out the hit.

Two other suspects were arrested in Spain and Curacao on the same day.

Before his shooting, Mr de Vries acted as an adviser and confidant for a witness in the trial of the alleged leader and other members of a crime gang that police described as an “oiled killing machine”.

The witness’s brother and his lawyer were both murdered.

The suspected gangland leader, Ridouan Taghi, was extradited to the Netherlands from Dubai, United Arab Emirates, in 2019 and is awaiting verdicts in his trial.

Prosecutors also want a life sentence for his alleged involvement in a string of murders.

He has not been charged in connection with Mr de Vries’ killing.