Michael Dreeben, the longtime U.S. Justice Department appellate lawyer who was a criminal-law expert on the special counsel’s team investigating Russia’s election interference, is retiring from federal government service.

Dreeben, a deputy U.S. solicitor general and career civil servant, will not return to the Justice Department’s solicitor general office, where he had worked for 30 years and earned a reputation as the Justice Department’s preeminent expert on criminal law.