The lowest level of investigative activity is the "prompt and extremely limited checking out of initial leads," which should be undertaken whenever information is received of such a nature that some follow-up as to the possibility of criminal activity is warranted. This limited activity should be conducted with an eye toward promptly determining whether further investigation (either a preliminary inquiry or a full investigation) should be conducted.
The next level of investigative activity, a preliminary inquiry, should be undertaken when there is information or an allegation which indicates the possibility of criminal activity and whose responsible handling requires some further scrutiny beyond checking initial leads. This authority allows FBI agents to respond to information that is ambiguous or incomplete. Even where the available information meets only this threshold, the range of available investigative techniques is broad. These Guidelines categorically prohibit only mail opening and nonconsensual electronic surveillance at this stage. Other methods, including the development of sources and informants and undercover activities and operations, are permitted in preliminary inquiries. The tools available to develop information sufficient for the commencement of a full investigation, or determining that one is not merited - the purpose of a preliminary inquiry - should be fully employed, consistent with these Guidelines, with a view toward preventing terrorist activities.
Whether it is appropriate to open a preliminary inquiry immediately, or instead to engage first in a limited checking out of leads, depends on the circumstances presented. If, for example, an agent receives an allegation that an individual or group has advocated the commission of criminal violence, and no other facts are available, an appropriate first step would be checking out of leads to determine whether the individual, group, or members of the audience have the apparent ability or intent to carry out the advocated crime. A similar response would be appropriate on the basis of non-verbal conduct of an ambiguous character - for example, where a report is received that an individual has accumulated explosives that could be used either in a legitimate business or to commit a terrorist act. Where the limited checking out of leads discloses a possibility or reasonable indication of criminal activity, a preliminary inquiry or full investigation may then be initiated. However, if the available information shows at the outset that the threshold standard for a preliminary inquiry or full investigation is satisfied, then the appropriate investigative activity may be initiated immediately, without progressing through more limited investigative stages.
The application of these Guidelines' standards for inquiries merits special attention in cases that involve efforts by individuals or groups to obtain, for no apparent reason, biological, chemical, radiological, or nuclear materials whose use or possession is constrained by such statutes as 18 U.S.C. 175, 229, or 831. For example, FBI agents are not required to possess information relating to an individual's intended criminal use of dangerous biological agents or toxins prior to initiating investigative activity. On the contrary, if an individual or group has attempted to obtain such materials, or has indicated a desire to acquire them, and the reason is not apparent, investigative action, such as conducting a checking out of leads or initiating a preliminary inquiry, may be appropriate to determine whether there is a legitimate purpose for the possession of the materials by the individual or group. Likewise, where individuals or groups engage in efforts to acquire or show an interest in acquiring, without apparent reason, toxic chemicals or their precursors or radiological or nuclear materials, investigative action to determine whether there is a legitimate purpose may be justified.