1. A forensic system configured to acquire digital information recorded on a plurality of computers or a server to analyze the acquired digital information, the forensic system comprising: a digital information acquiring unit configured to acquire digital information containing digital document information composed of a plurality of document files, and to acquire user information about users using the plurality of computers or the server; a recording unit configured to record therein the digital information acquired by the digital information acquiring unit; a display unit configured to display the recorded digital information; a user-specifying information setting unit configured to set user-specifying information showing which one of users contained in the user-specifying information each of the plurality of document files is related with, and configured to cause the recording unit to record the set user-specifying information, via the display unit; a user selecting unit configured to select at least one user via the display unit; a searching unit configured to search a document file where the user-specifying information corresponding to the selected user was set; an additional information setting unit configured to set additional information showing whether or not the searched document file is related with litigation; and an output unit configured to output the document file which is related with the litigation, based on the additional information.