A Dutch art detective dubbed the "Indiana Jones of the Art World" has recovered another six paintings, including a portrait of William of Orange and the first depiction of a seventh-century king.

Art sleuth Arthur Brand made headlines around the world last month when he recovered a stolen Van Gogh stuffed in an Ikea bag, and he believes that widely publicized success is leading to more discoveries.

Thieves made off with the latest six paintings from the town hall of Medemblik, in the north of the country, last month.

While the monetary value of the haul is not huge — around 100,000 euros ($105,000) — the paintings are considered of great historical significance, including the earliest known portrait of Radbod, king of the Frisians from 680AD.

Brand was sitting at home on Friday night watching football when the doorbell rang and a man in a van asked him for help to unload some merchandise.

"I asked him, 'what are we going to unload?'. He said with a smile, 'well, the paintings of Medemblik'," Brand recounted.

After the initial burglary in September, Brand had been widely quoted in the Dutch press as saying the thieves should have stolen six bikes, as these would be easier to resell.

Those comments, plus the publicity surrounding the Van Gogh recovery, probably led the thieves to simply hand the paintings back, explained Brand.

"In some cases, they burn them, just to get rid of the evidence because they find out they cannot sell them," he told AFP.

"So I'm very thankful that they decided to do the right thing. Stealing is wrong, but if you return it, at least you do something right," he added.

Now Brand is hoping that the momentum from the Van Gogh will lead to another prize recovery — a masterpiece by Frans Hals called "Two Laughing Boys".

He also has his eye on recovering work from the Isabella Stewart Gardner Museum in Boston, where paintings worth an estimated $500 million from the likes of Vermeer, Manet, and Rembrandt were stolen in 1990.

The authorities in Medemblik had offered a reward of 10,000 euros for the safe return of the paintings but this has gone unclaimed.

Brand said he would not be collecting the cash himself.

"I told them to give me a good book voucher," he quipped.

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© Agence France-Presse