With regard to legal representatives, the agreement must be approved by the Supervisor Officer, in consultation with the Chief Federal Prosecutor (CFP). The Crown prosecutor should also assess the relative strength of the case for criminal prosecution, with or without the testimony of the information provider or other evidence, and be satisfied that the person is able and willing to provide reliable evidence on important aspects of the case. The lawyer should also consider whether the same evidence can be obtained from another source that does not require any guarantee of immunity. The fact that the testimony of the information provider confirms unconfirmed evidence from other witnesses may make the justification for immunity sufficiently important. If you have included, concealed, and retained evidence as part of a federal criminal investigation, such behavior may be contrary to 18 United States Code 641.