The man dubbed ‘Indiana Jones of the art world’ says the paintings can ‘become a burden’

The ring at the door of the modest east Amsterdam apartment came late in the day on Thursday 14 March. On the doorstep stood two men “with contacts in the underworld”, Arthur Brand recalls, and with them a large, rectangular package.

Eagerly, Brand removed the covering and examined the contents: Buste de femme (Dora Maar), a portrait by Pablo Picasso of his mistress. Unsigned because it was never sold by the painter, it bore in its bottom-left corner the date he completed it, 26 April 1938, and was worth an estimated €25m (£21.5m).