Olympus Corp. said Monday that CEO Stefan Kaufmann has stepped down from his post following an allegation that he purchased illegal drugs. The Japanese company launched an investigation after hearing the allegation and its board unanimously determined that its CEO “likely engaged in behaviors that were inconsistent” with its code of conduct, it said. Following the decision, the company asked Kaufmann to resign and he accepted, Olympus said. Chairman Yasuo Takeuchi will double as chief executive for the time being. Police are also looking into the case after the optical precision equipment repo…