after the firm in charge of arranging tsien's move back to china tipped off u.s. customs that some of the papers encountered among his possessions were marked "secret" or "confidential," u.s. officials seized them from a pasadena warehouse. the u.s. immigration and nationalization service issued a warrant for tsien's arrest on august 25. tsien claimed that the security-stamped documents were mostly written by himself and had outdated classifications, adding that, "there were some drawings and logarithm tables, etc., which someone might have mistaken for codes." included in the material was a scrapbook with news clippings about the trials of those charged with atomic espionage, such as klaus fuchs. subsequent examination of the documents showed they contained no classified material.