Trust me. It can be a harrowing and anxiety-filled experience for the federal government to send its agents from the Justice Department to come and speak to you. You should not take this situation lightly. They are highly trained interrogators and investigators and you should have a skilled attorney that has sat through, appeared in these type interviews to assist you in telling the truth, if indeed a statement is given, and also protecting you from further harm by you giving a statement that may be in contra to a Fifth Amendment protections against self-incrimination, and also facts being given that may subject you to suborn perjury and expose you to obstruction of justice and/or lying to a federal officer, charges and/or indictment. 

Federal law enforcement intervention and involvement in a case should always be taken seriously. You cannot talk your way out of them not charging and/or investigating you. Some of the best have tried and many have failed. Be sure to get an experienced attorney on board and always understand that never speak to them without a lawyer no matter how innocent it may be. After their contact with you make sure to shut down any email, phone call, conversations going forward until you speak with your lawyer and also understand that silence not only is golden in preserving your rights; that silence may save you from the anxiety of being charged and being actually indicted on a federal case. 

Innocent people do get indicted and people, by talking too much, indict themselves from their statements because they are not properly represented or not represented at all in this seemingly preliminary phase of a federal agent's investigation. It is difficult to battle the government's sophistication and investigative techniques without the support and protection of legal counsel. Remember: 

The truth is not always the truth, especially if the government has their own version of what the truth is or it isn't in harmony of your perceived truth.