The 16 year old was transported to a local hospital in two ambulances after the tragic 2 January (09) incident as the emergency medical technicians (EMTs) changed shifts halfway.
Marcus Garvey, who took over caring for Jett from one of the accused paramedics in the Travolta extortion case, claims the boy showed signs that he had been dead for some time when he was examined.
Garvey tells the National Enquirer, "After 17 years of experience as an EMT, I am sure the boy was dead long before he was found at his parents' condo, and the fight to save him was over before it began.
"When we took over, I opened the boy's eyes and shined a light to gauge pupil reaction. The pupils were fully dilated and fixed, indicating he was dead. His body was cold and rigor mortis had set in. Pooling of the blood in part of the body told me he had been dead seven or eight hours."
Garvey puts the blame for the delayed emergency call on Jett's two carers Eli Wheaton and Jeff Kathrein, who he alleges were desperate to cover up the scandal after spending the night partying: "We heard stories about the nannies partying at the beach the night before (Jett's death), and the first ambulance man on the scene said he was told they didn't hear the monitor that was supposed to alert them that Jett was up and going to the bathroom."
And Garvey believes the autistic boy died at least seven hours before Travolta and Preston were woken up and told of Jett's condition at 10am local time: "With all my training and experience, I believe Jett died around three or four in the morning. He must have been alone. We know he fell and hit his head.
"I don't think for a moment John is part of it (the cover-up). But I think employees who were supposed to monitor Jett's movements must have been desperate to try to show that he was still alive when he was found at 10am. Perhaps if the monitor had been heard in time, he could have been saved."
Former Bahamian Senator Pleasant Bridgewater and paramedic Tarino Lightbourne, who tended to the boy immediately after the attack, are currently on trial in the Bahamas on charges of extortion.
They are accused of conspiring to release a document containing information about Jett's death in a $25 million (£17.2 million) bribery plot against the Travoltas - claims they deny.