The partly clothed body of Barry Trigwell, 44, was found floating in a bath after being bludgeoned to death at his home in Walmley, Birmingham, on 8 February. His skull was fractured.
Mr Trigwell has worked abroad on many occasions, including snatching back children for parents living in Britain. He was known by some he crossed as "Barry the bastard".
Detectives hunting Mr Trigwell's killer yesterday issued the names of two men - Lorenz Sundkvist and Paul Ras - who they want to interview. They have warned the public not to approach the pair, who may be dangerous.
The two men were described as having strong South African accents and appeared to be using fake moustaches to disguise their appearances. Their names may also be false.
The men have made two visits to Britain this year. The first trip was from 22 to 29 January, the second was from 3 to 8 February. They have stayed in hotels in London, Birmingham, and Lichfield in Staffordshire. Police said they spent most of their time in their hotel rooms.
Detective Superintendent Ken Evans, who is leading the inquiry, said: "We are anxious to trace these two men in connection with the brutal killing of Mr Trigwell. However I cannot say if Mr Trigwell knew these two men or if they were hired hit men."
He added: "There is a strong possibility that the men could still be in a hotel somewhere in this country. They did not leave their rooms very often and as businessmen that might strike people as unusual," he said. Police still do not know the movements of the two men between 6 and 7 February this year.
At the time of his death Mr Trigwell ran a franchise of one of Britain's largest private detective agencies, Nationwide Investigations, at its offices in Birmingham. Former colleagues said that he had made several enemies through his work.
Mr Sundkvist was described as a 6ft 2 white male with a Mediterranean complexion, and aged about 40. He is of medium build with white or grey hair. Mr Ras was described as a 5ft 7 white male of similar complexion and aged about 35.Reuse content