Samuel Colpepper is the main murder victim of So It Goes (episode).
After his boss, Angus Clarke, uncovered evidence that his protégé, Gareth Godfrey, had arranged for six Naval officers to be killed in a manner that was made to look like an accident and replace them with Albanian-American members of the same Albanian mafia that he was running, he stayed behind in America, and was on his way over to the NCIS compound to deliver this information.
While in Washington, he did a shopping spree and also planned to visit the Smithsonian.
However, before he could get to the NCIS compound, a member of the Albanian mafia used a stolen missile launcher to blow up his rental car in the middle of a call.
Because the car was registered in Angus Clarke's name, the NCIS medical examiner, Donald Mallard, initially thought the man was actually his old friend, Clarke, although he soon discovered otherwise when it was revealed that "Clarke's" corpse had a full set of teeth (Clarke had his incisors knocked out of him by Ducky in a bar fight the day before he shipped off), with his actual identity being discovered shortly thereafter.
Because of the hard-drive being damaged from the explosion, only half of the list was uncovered, although the full list was emailed from Clarke's office computer by NCIS Agent Eleanor Bishop who had gone to the UK with Mallard to investigate.