Detectives are still seeking a motive for the murders on board the ketch which was moored off a deserted beach on the island of Barbuda, near Antigua, but it has been suggested the victims may have stumbled across a drug-smuggling operation.
The bodies of Bill Cleaver, 58, his wife Kathy, 50, and rew members Ian Cridland, 35, and Thomas Williams, 22, were found around a small table in a blood-spattered cabin. They had been bound, gagged and stabbed repeatedly in the face, head, neck and shoulders.
Detective Superintendent Michael Lawrence, of Scotland Yard, who is leading the inquiry, said they had yet to carry out post-mortem examinations or a detailed search of the yacht, but it appeared the victims had been tortured to death. 'The initial reaction is that it was probably quite a long and lengthy death for them. One can only assume they died one at a time and therefore were in the unfortunate situation of watching their own friends and colleagues die,' he said.
He added that they had suffered horrendous injuries, and it appeared they had been stabbed many times with a marlinspike and a knife found at the scene.
Mr Lawrence, one of three Scotland Yard detectives working with local officers, said he could not dismiss any theory yet, but the four appeared to be innocent victims and to have no link with drugs.
Antigua's deputy police commissioner, Alvin Goodwin, has said police were 'looking in the direction' of a drugs connection.
The party were last heard from at 6pm on Thursday when they telephoned an acquaintance in Antigua to say they had spent the day snorkelling in Barbuda and would be back on Monday.
Mr Lawrence said he believed they had been murdered later that night by at least two people.
The alarm was raised on Monday after holidaymakers on another yacht became suspicious after seeing no signs of life for two days.
Mr Cleaver and his wife, from Jersey, were on holiday in the 65ft yacht, which belongs to the chairman and managing director of the company he worked - micro- computer dealers Computacenter.
Mr Cridland and Mr Williams, both from the Southampton area, were the full-time crew.
Mr Lawrence said they expected to begin the post mortem examinations on Friday and they were likely to take three days.
He said the yacht had been sealed and would be given a detailed forensic examination after the post mortem examinations had been completed.
A British forensic expert was flying to Antigua yesterday to help with the investigation.