A Romanian man who visited the Drents Museum shortly before historic artefacts were stolen in an armed heist may have been on a reconnaissance mission, police documents show.

Andrei B., 38, was questioned as a witness in January after he was identified on security cameras at the museum in Assen five days before the robbery, RTL Nieuws reported, citing police documents.

He entered the museum without a ticket, carrying a sports bag on his shoulder, and wandered around the exhibition “Dacia: Empire of Gold and Silver” before being escorted out by security.

Thieves broke into the museum using a firework bomb early on the morning of January 25 and made off with the golden helmet of Cotonesti and three gold armbands. The solid gold helmet, which dates from 500BC, has an insurance value of almost €6 billion.

Three Dutch men are due to appear in court on Thursday for a procedural hearing in the case, but police believe the robbery was organised by the Romanian underworld.

B. told police he went to the museum believing it was a Dacia car showroom, but instead stumbled on the exhibition of priceless artefacts from his native country.

But police believe he was surveying the site as part of the preparations for the venue. International police enquiries revealed he was a regular customer at two restaurants in southern Germany that were frequented by “a team of thieves who steal artefacts to order”.

B. was also arrested last year and given a four-week prison sentence for stealing a nose hair trimmer from a Kruidvat store in Assen. He was not arrested in connection with the museum theft.

The three men in police custody are all from Noord-Holland and aged 36, 35 and 21. RTL Nieuws earlier reported that they were connected to the banned Hardliners biker gang, operating under instructions from criminals in Romania.