By Sarah N. Lynch and Chris Prentice WASHINGTON (Reuters) -The U.S. Justice Department has tapped a seasoned computer crimes prosecutor to lead its new national cryptocurrency enforcement team and announced on Thursday that the FBI is launching a unit for blockchain analysis and virtual asset seizure. The creation of the “virtual asset exploitation” unit at the FBI comes on the heels of the Justice Department’s largest-ever financial seizure. Earlier this month, it charged a married New York couple with allegedly laundering bitcoins now valued at over $4.5 billion that were stolen in the 2016 …