His last two years in this position were spent in the Hardcore Gang Division of the Bureau of Special Operations, where he prosecuted gang-related murders.

From 1999 to 2001, Prosper was detailed to the State Department where he served as the Special Counsel and Policy Adviser to the previous Ambassador-at-Large for War Crimes Issues.

Secretaries of State Colin Powell and Condoleezza Rice and advised the President of the United States, Secretary of Defense, Attorney General, National Security Advisor, Chairman of the Joint Chiefs of Staff, Director of the Central Intelligence Agency, White House Counsel, and other senior U.S. government officials.

From 2008-2012, Ambassador Prosper was elected to the United Nations' Committee on the Elimination of Racial Discrimination, where he served as Vice-Chairman for the last two years of his service.

Currently, Prosper holds the position of Partner in the Los Angeles office of ArentFox Schiff LLP, where he has handled several high-profile cases.

These include advising and representing the Democratic Republic of Timor-Leste on matters related to the Petroleum sector, investment and infrastructure development; successfully negotiated the release of an American citizen detained in the Islamic Republic of Iran through repeated travels to Iran and engagement with senior Iranian officials; and advises and represents the government of Rwanda on a range of matters including international arbitration, litigation, and contract negotiation, among others.