This study focuses on privacy issues concerning personal data held by third parties during criminal investigations. The development of information technology has made it possible to collect and store vast amounts of information. Since data held by third parties are often provided to investigating authorities without the data subject’s knowledge, serious privacy issues are a concern. There are two possible approaches to protecting the rights of the individual in such a situation. One relates to the restriction of investigating authorities and the other concerns the confidentiality obligations of data controllers. This study compares the relevant legislation on the privacy of personal data held by third parties and criminal investigations in the United States, the European Union, and Japan to propose appropriate solutions to address data privacy concerns. Specifically, the main recommendations of this study are that investigating authorities should be subject to certain restrictions and greater transparency requirements when processing personal data and that data controllers should be subject to greater confidentiality obligations.