Mondrian, one of the most important artists of the 20th century, is famous for his abstract compositions of black lines and rectangles filled with bright colors.
The museum said eight of his works surfaced there in 1950. While it is not clear how they came there, the museum said it's possible that the artist himself gave them the works in 1929, for an exhibition that never took place. Mondrian never reclaimed the works and after 1950, the museum swapped four of the artworks for works by other artists, it said. The remaining four Mondrian works are still in the Krefeld museum's possession.
Schnabel, the lawyer for the Mondrian heirs, said it would have been "hopeless" for Mondrian to try to reclaim his works because they were deemed "degenerate art" after the Nazis took power in Germany in 1933. Mondrian himself left Europe for the United States and died in exile in New York in 1944.
The museum said it would task an expert with shedding light on the disputed history of the eight works.