Initially proscribed by the Nazis, clandestine cultural activities started to take place in early December, largely to relieve the tedium and poverty in which the first inmates found themselves, but also as a direct result of the first executions. Nine men from Klein's AK group were caught for the ‘offence’, punishable by death, of smoking or of smuggling out letters to their loved ones. The writer Mirko Tuma, imprisoned in the ghetto from its early days, explains the connection between the first cultural activities and the arrests:

Klein's friends and fellow musicians, among them the pianist and conductor Rafael Schächter and the violinists Karel Fröhlich and Heini Taussig, as well as other musicians and actors, were there with him from the start. There is no evidence that he contributed to any of the early informal concerts which took place in the barracks in those first few days and, as a piano was not yet available for the prisoners, it is unlikely that he did. But some of the other musicians brought their instruments with them, although strictly it was not permitted.3 Even so, by the end of December, the Council of Elders reached an agreement with their captors, and the Nazi authorities sanctioned what were known as Kammeradschaftsabende (Fellowship Evenings).