Celebrity Dutch crime reporter Peter R de Vries. (Photo: Remko de Waal/ANP/AFP/Getty Images)

De Vries, 64, was well-known for his television programmes, in which he often worked with victims' families and tirelessly pursued unsolved cases.

He had received threats in the past from the criminal underworld in connection with his work.

Two men who were arrested on a highway shortly after the July 6 shooting, one of them a Polish national, remain in custody as murder suspects.

Dutch Prime Minister Mark Rutte vowed to track down whoever was behind the shooting of a man he described as a determined and fearless reporter.

The head of the European Commission, Ursula von der Leyen, said more must be done to protect investigative journalists.

De Vries won an international Emmy Award in the current affairs category in 2008 for his work investigating the 2005 disappearance of US teenager Natalee Holloway in Aruba.