German police have arrested a man in connection with October’s art heist from Rotterdam’s Kunsthal museum, Dutch media report on Thursday afternoon.

The Cologne public prosecution service says the man was attempting to blackmail the Triton foundation, which owns six of the paintings, news agency ANP reported. The foundation lent the works to the Kunsthal as part of an exhibition to celebrate the gallery’s 20th anniversary.

It is not clear how much money the man was demanding or if he was bluffing, ANP said. No trace has been found of the paintings since the October heist.

The man, a 46-year-old German national, is said to have met representatives of Triton at the end of last year in Cologne. Police got wind of the meeting and started an investigation, ANP said.

Three Romanian nationals face trial in Romania for stealing the paintings, which include works by Matisse, Monet and Picasso. A 19-year-old Romanian woman has also been arrested in Rotterdam.