Police have additionally booked about 100 doctors suspected of receiving illegal kickbacks from a drugmaker, a senior police official said Monday.The investigation began after allegations arose that as many as 1,000 doctors received kickbacks in cash and other rewards from the Korean Drug Co. and 22 people had already been booked for investigation, including 14 doctors and eight Korean Drug officials."The number of doctors booked could go up as the investigation proceeds," the Seoul Metropolitan Police Agency official said, adding they have questioned about 70 people, including Korean Drug officials and salesmen, as witnesses so far.Police launched the investigation following a request from the Anti-Corruption and Civil Rights Commission, and have since raided the headquarters of the pharmaceutical company in April and obtained a computer file, named "BM," or black money, which details kickback offerings.Police are expanding their investigation into the broader medical circles and raided a general ho spital in Anyang, south of Seoul, last month. The Seoul Metropolitan Police Agency is also investigating six similar kickback cases at the request of the health ministry.The Korea Medical Association (KMA), the country's largest doctors' association, has claimed the probe was part of retaliatory measures against the ongoing collective action by trainee doctors, but the police official dismissed it as a "completely separate" matter.Source: Yonhap News Agency