Authorities in Antigua say Avie Howell, convicted of the murder of Welsh newlyweds Ben and Catherine Mullany, and another escaped prisoner are considered armed and dangerous and should not be approached.
It is understood Howell is due to stand trial later this year, accused of two other people.
Antiguan police corporal Frankie Thomas assured they were doing all they could to find them.
He said: "We have not yet had any confirmed sightings but we have had a lot of calls from the public. Antigua is a very small island and something does not stay a secret here for long."
"We remain very optimistic and confident we will find Avie Howell."
He urged anyone with information on Howell's whereabouts to contact police.
The parents of Ben Mullany, who was murdered along with his new wife Catherine on honeymoon in Antigua, say they want his escaped killer back in prison as soon as possible.
Avie Howell, one of two men convicted of murder and sentenced to life in prison in 2011, has now escaped from prison on the Caribbean island.
Marilyn Mullany said: "I'm shocked at the way he has managed to escape."
Cynlais Mullany said: "We hope he is caught as soon as possible. We don't want him running loose."He has caused enough damage as it is and we want him back in prison as soon as possible."It seems incredible that he has managed to get over a 30ft wall to escape."
Avie Howell and Kaniel Martin, both from Antigua, were sentenced to life in prison in December 2011, after being found guilty of murdering Ben and Catherine Mullany on their honeymoon on the island in July 2008.
The 31-year-olds, from Pontardawe, celebrated their wedding in Cilybebyll just over a fortnight earlier.
They were both shot in the head in their chalet at the Cocos Hotel, while their killers escaped with their mobile phones, a digital camera and some cash.
Catherine died instantly, while Ben was flown home but died in hospital in Swansea a week later.
Howell and Martin were also found guilty of shooting a local shopkeeper.
Last year, Howell was handed an additional four-year sentence for a burglary he carried out just weeks before murdering Ben and Catherine Mullany.