Nothing in this section shall be construed as indicating an intent on the part of Congress to prevent any State, any possession or Commonwealth of the United States, or the District of Columbia, from exercising jurisdiction over any offense over which it would have jurisdiction in the absence of this section, nor shall anything in this section be construed as depriving State and local law enforcement authorities of responsibility for prosecuting acts that may be violations of this section and that are violations of State and local law. No prosecution of any offense described in this section shall be undertaken by the United States except upon the certification in writing of the Attorney General, the Deputy Attorney General, the Associate Attorney General, or any Assistant Attorney General specially designated by the Attorney General that in his judgment a prosecution by the United States is in the public interest and necessary to secure substantial justice, which function of certification may not be delegated.

Nothing in this subsection shall be construed to limit the authority of Federal officers, or a Federal grand jury, to investigate possible violations of this section.