Police have appealed for anyone who knew Kevin Palmer in 1999 to come forward.
Detective Superintendent Paul Barton said: "Even after 15 years, the smallest piece of detail from a member of the public could prove to be an essential element in establishing a significant lead."
Witnesses or anyone with information are asked to contact the Hampshire Major Investigation Team at Southampton Central police station by phoning 101 and quoting Operation Arkholme. Anyone who wants to remain anonymous can call Crimestoppers on 0800 555 111.
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Three drug dealers have been sentenced to a total of 23 years after admitting they were key players in a multi-million pound drugs ring.