John Travolta was preparing last night to speak publicly for the first time about the death of his teenage son, as a witness in the trial of two people accused of trying to blackmail him for $25 million.

The actor, left broken by the loss of Jett, aged 16, during a family holiday in January, was expected to tell a court in the Bahamas that a local politician and a paramedic attempted to cash in on his grief in the days after his boy’s death.

Pleasant Bridgewater, a former senator in the Bahamas, and Tarino Lightbourne, one of the ambulance workers called to tend to the dying teenager after he fell and hit his head during a seizure, have pleaded not guilty to extortion charges.

Mr Travolta is due to give testimony to the jury of three men and six women about how the pair allegedly threatened to go public with a private document relating to Jett’s emergency care unless he paid them off.

Jett, who suffered from Kawasaki disease — a rare condition that inflames the blood vessels and affects only about one in every 100,000 children in the US — was found lying unresponsive on the bathroom floor of the family’s holiday home as they prepared to welcome guests for a new year house party.

A post-mortem examination concluded that he had died of a seizure, possibly hitting his head as he fell.

The extortion case relates to a document that Mr Lightbourne claims that Mr Travolta signed that day, releasing paramedics from liability after he asked them to drive his son to the airport — where his private jet was parked — rather than to a local hospital.

Reports leading up to the trial had said that Mr Travolta had not signed such a form. But a police inspector, Andrew Wells, the first witness to take the stand at the Bahamian New Providence Supreme Court yesterday, told the jury that Mr Lightbourne had told him that the star had signed it, fearing that Jett might get inferior medical treatment locally. Prosecutors say that Mr Lightbourne and Ms Bridgewater threatened to make the document public, demanding that Mr Travolta — a member of the Church of Scientology, which controversially advocates against conventional medical treatment — pay $25 million to keep it private.

“Contact was made with certain persons to communicate a threat to John Travolta,” said Bernard Turner, the chief prosecutor.

The case continued last night.

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