Dr Rau, a medical doctor and philanthropist who set up a hospital in the Congo, acquired more than 400 paintings and 220 sculptures from the 15th to 20th centuries. These works could be worth as much as several hundred million pounds. Dr Rau died in Germany two years ago, aged 79, leaving his collection to Unicef. Before and after his death there were legal disputes over his will. Last month it was announced that the Stuttgart state prosecutor has begun a manslaughter investigation, following a post-mortem which revealed high levels of toxins in his body. A touring exhibition of 90 works from the Rau Collection was shown at the Portland Art Museum in Oregon last August.