Criminal lawyers who handle federal criminal cases are known as federal criminal lawyers. As per the work or proceedings taken over by these criminal lawyers, they are divided into two categories. One group of the criminal lawyers works as federal prosecutors. Another group of lawyers defends people who are considered as criminals by the court. The prosecuting federal criminal lawyers are also commonly known as US attorneys. A criminal lawyer firm or professional, regardless of categories, must be well proficient and knowledgeable about criminal law that is enforced by the federal law enforcement authorities.