Mr. Van Grack, a national security prosecutor based at the Justice Department headquarters in Washington, has experience conducting espionage investigations.
The investigation stems from the work Mr. Flynn did for Inovo BV, a Dutch company owned by Mr. Alptekin, the Turkish businessman.
Trump campaign officials first became aware of a problem with Mr. Flynn’s business dealings in early November.
By Jan. 4, the day Mr. Flynn informed Mr. McGahn of the inquiry, the Justice Department was investigating the matter.
Current and former American officials said that, on the calls, Mr. Flynn discussed sanctions that the Obama administration had imposed on Russia for disrupting the November election.
After news of the calls became public, Mr. Flynn misled Mr. Pence about what he had discussed with Mr. Kislyak, telling him that the two had only exchanged holiday pleasantries.
Since the Russians knew that Mr. Flynn had lied to the vice president, she said, they might have leverage over him. »
