If you are contacted by the federal authorities in relation to a criminal investigation, the first thing you must attempt to determine is if you are being contacted as a potential witness or as a suspect. The second thing you must determine is what statements you can safely make to the authorities without potentially falling into a trap, such as being charged with lying to federal agents. Consider for example the case of Martha Stewart, who was acquitted of any direct criminal wrongdoing but spent time in prison for making false statements to federal investigators.
A federal criminal defense lawyer can help you assess the nature and purpose of the investigation, and why you are being approached. While you should expect your lawyer to instruct you to provide honest answers to any questions from the federal authorities, your lawyer may be able to guide you around any potential traps or pitfalls. When appropriate, a federal criminal defense lawyer can be present during any questioning, act as an intermediary between you and the investigating authorities, or advise you to exercise your Fifth Amendment privilege against self-incrimination. If appropriate, a federal criminal defense lawyer may be able to work out a deal where you will cooperate with the investigation, in return for more favorable treatment when the investigation is concluded. In appropriate cases your lawyer may also be able to secure a letter of declination, in which the U.S. attorney formally declines to prosecute you in relation to a particular offense or investigation.