incarcerated person for whom such contents are retained under the following circumstances: (1) Attorney general The Attorney General may only access retained contents if necessary for the purpose of creating and maintaining the program or system, or any modification to the program or system, through which an incarcerated person sends or receives electronic communications. The Attorney General may not review retained contents that are accessed pursuant to this paragraph. (2) Investigative and law enforcement officers (A) Warrant (i) In general Retained contents may only be accessed by an investigative or law enforcement officer pursuant to a warrant issued by a court pursuant to the procedures described in the Federal Rules of Criminal Procedure. (ii) Approval No application for a warrant may be made to a court without the express approval of a United States Attorney or an Assistant Attorney General. (B) Privileged information (i) Review Before retained contents may be accessed pursuant to a warrant obtained under subparagraph (A), such contents shall be reviewed by a United States Attorney to ensure that privileged electronic communications are not accessible. (ii) Barring participation A United States Attorney who reviews retained contents pursuant to clause (i) shall be barred from— (I) participating in a legal proceeding in which an individual who sent or received an electronic communication from which such contents are retained under subsection (b) is a defendant