They dismissed suggestions that Howard Bates, 44, a former RAF pilot from Hawkhurst, Kent, was involved with drug barons and said he was shot dead because he had discovered a huge fraud.
Mr Bates went to the United States on a two-day trip in February 1991, telling his wife he planned to confront a man who had swindled him out of hundreds of thousands of pounds.
His body was discovered in swampland late last week. He was apparently lured to the spot, behind a factory, and shot in the back of the head, police said. Albert Lucio, 32, and Wayne Merced, 26, are being held in Miami's Dade County jail charged with murder. Lucio was Mr Bates's business partner in the Miami company Bolden Surgical Products.
Police are also searching for a 29-year-old woman, Magaly Carr, an employee of the company and Merced's girlfriend.
A Miami police spokesman said yesterday: 'Lucio was scamming Mr Bates from the beginning and took about dollars 1m of his money over an eight-month period.
'Merced was not involved in the fraud but was involved in the murder. The motive was that these people were stealing Mr Bates's money and using it for personal gain, and we think Mr Bates realised this was going on. He came over in February 1991 to confront his business partner Lucio.'
Reports that Mr Bates may have been involved with Miami drug barons had been ruled out.
Jarratt Crawford, a Miami detective, told BBC Radio Kent that Mr Bates 'had lost money which he was attempting to recoup'.
He added: 'They had convinced him they had it invested. It was to purchase his side of the business but that was admitted to be a fraud - there was no investment. And they basically lured him over here. Of course, their statement was that it was not intentional that the shooting occurred, but my feeling is otherwise.'
Mr Bates was co-founder 12 years ago of South East Computers, a computer dealership based in Hastings, East Sussex.
David Turner, technical director of South East Computers at the time of the disappearance, said Mr Bates put money into Bolden Surgical Products after South East Computers was sold to a technology group. According to Miami police, from June 1990 Mr Bates invested pounds 500,000 in Bolden.
Lucio reported him missing on 9 February 1991. Police became suspicious after Mr Bates's passport and all his belongings were found in his hotel room.