((a)) Whoever escapes or attempts to escape from the custody of the Attorney General or his authorized representative, or from any institution or facility in which he is confined by direction of the Attorney General, or from any custody under or by virtue of any process issued under the laws of the United States by any court, judge, or magistrate judge, or from the custody of an officer or employee of the United States pursuant to lawful arrest, shall, if the custody or confinement is by virtue of an arrest on a charge of felony, or conviction of any offense, be fined under this title or imprisoned not more than five years, or both; or if the custody or confinement is for extradition, or for exclusion or expulsion proceedings under the immigration laws, or by virtue of an arrest or charge of or for a misdemeanor, and prior to conviction, be fined under this title or imprisoned not more than one year, or both.

((b)) Whoever escapes or attempts to escape from the custody of the Attorney General or his authorized representative, or from any institution or facility in which he is confined by direction of the Attorney General, or from any custody under or by virtue of any process issued under the laws of the United States by any court, judge, or magistrate judge, or from the custody of an officer or employee of the United States pursuant to lawful arrest, shall, if the custody or confinement is by virtue of a lawful arrest for a violation of any law of the United States not punishable by death or life imprisonment and committed before such person’s eighteenth birthday, and as to whom the Attorney General has not specifically directed the institution of criminal proceedings, or by virtue of a commitment as a juvenile delinquent under , be fined under this title or imprisoned not more than one year, or both. Nothing herein contained shall be construed to affect the discretionary authority vested in the Attorney General pursuant to .