In 1974, Merletti joined the Secret Service as a special agent assigned to the Philadelphia Field Office later transferred to the New York City Field Office. In 1982, Merletti was transferred to The Office of Protective Operations in Washington DC. He volunteered for the newly established United States Secret Service’s
Counter Assault Team (CAT). He completed training and received his designated CAT Operator Number in May 1982. CAT is a specialized tactical unit of the Secret Service, providing tactical support to the Presidential Protective Division; specializing in counter-ambush tactics and close-quarters combat (CQB). On April 29, 1993, The
United States Department of the Treasury's Secretary
Lloyd Benson and
Assistant Secretary Of The Treasury for the Office of Enforcement,
Ronald K. Noble, announced its plans to examine the
Bureau of Alcohol Tobacco and Firearm's (ATF)
execution of search and arrest warrants for
David Koresh and other
Branch Davidians at their compound near
Waco, Texas on February 28, 1993. Benson and Noble selected Merletti, then the Secret Service's Deputy Assistant Director, as the "Assistant Project Director" to oversee the investigative team charged with the analysis and assessment of whether ATF's procedures, policies, and practices were adequate and whether they were followed up until the time ATF decided to raid the compound. The review "Report of The Department of the Treasury on the Bureau of Alcohol, Tobacco, and Firearms, Investigation of Vernon Wayne Howell also known as David Koresh" of the incident was assessed as being extensively and "brutally detailed" and a "biting review" of the incident. Merletti also defended this document to the Joint House Subcommittee regarding the Waco investigation. The overall report and his response to this was widely considered a courageous and candid evaluation of the events that took place. Throughout his tenure with the agency he served for Presidents
Gerald Ford,
Jimmy Carter,
Ronald Reagan,
George H. W. Bush, and
Bill Clinton. He also held the position of Special Agent in Charge of Presidential protection during the Clinton Administration, which made him responsible for the physical security of the President and First Family. He was also in charge of supervising security arrangements for Presidential visits to dangerous high security environments including
Israel,
Syria,
Kuwait, and
Saudi Arabia during
Operation Desert Shield. Following his time in the Secret Service, he has remained connected to the military and Secret Service. In October 2017 and again in September 2018, Merletti gave presentations in North Carolina, at Fort Bragg's JFK Center for the Special Warfare Non-commissioned Officers Academy highlighting his Special Forces training and experiences, and how he applied that training and experience to the United States Secret Service. Other co-presenters for the event included retired Special Forces legends
Billy Waugh and
Felix Rodriguez. Merletti, along with Waugh, is currently a regular guest lecturer for various Special Forces basic and advanced courses. Both are highlighted in best selling author
Annie Jacobsen's book
Surprise, Kill, Vanish: The Secret History of CIA Paramilitary Armies, Operators, and Assassins In March 2019, Merletti was the Keynote Speaker for the United States Secret Service's Counter Assault Team graduating class. The 2020 Book: "They Were Soldiers" by
Joseph L. Galloway and Marvin Wolf describes the contribution that Merletti made as an officeholder following his initial service as a Vietnam veteran who returned home from the "lost war". ==Clinton trial==