Michael and Thelma King were found slain outside their St. Maarten vacation home in September.
The third suspect in the killing, a 20-year-old identified as J.J.W., was arrested Thursday by St. Thomas police, WCIV-TV, Mount Pleasant, S.C., reported.
Prosecutors said J.J.W. flew to St. Thomas sometime during the week, but has been extradited to St. Maarten.
Authorities previously arrested a Jamaican security guard and a 17-year-old for the killings, WSOC-TV, Charlotte, N.C., reported.