Dutch investigators are examining the involvement of Romanian organised crime in the Drents Museum gold heist, in which thieves stole a unique gold helmet and three armbands, officials in Romania have confirmed.

RTL reported earlier this week that there are connections between the case, a banned Dutch motorbike gang, and Romanian criminals.

Romania’s chief prosecutor Alex Florenta told the broadcaster on Wednesday that the Romanian angle is under investigation. And according to news website G4Media.ro, a team of Romanian investigators travelled to the Netherlands on 15 May to assist with the case.

RTL said on Wednesday morning that the artefacts were stolen on the orders of a Romanian criminal who hoped to use the gold to negotiate a reduced sentence. The job, RTL said, was handed to a Dutch motorbike gang known as the Hardliners, who then recruited the burglars.

The broadcaster said its information is based on multiple sources close to the investigation and to criminal networks.

The Dutch public prosecution department declined to comment in detail on the claims, stating only that “nothing can be said” about whether someone commissioned the heist.

The golden helmet of Coțofenești and three gold bracelets were taken during an overnight break-in at the museum on 24 January, in which the burglars used explosives and hammers to gain entry.

Seven people have been arrested, two of whom have appeared in court, but the helmet – which dates from the fifth century BC and has an insurance value of €5.8 million – is still missing.