Emergency specialist Larry Wans made an extraordinary claim after he tried not to seriously question him.
Fans, who wrote the MH370: Mystery Solved, told Daily Star: "Passengers arrive in southern India, and they are on the seabed in an inundated and intact felayage."
The expert said he had evidence of where the Boeing 777 dropped, but it was still not seriously concerned.
He said: "I honestly believed that during an official investigation team, when the official investigation team members saw the facts that we discovered and interpreted precisely, they would change the thought of what they thought was the case with the MH370.
"Sorry and disappointing, I was wrong."
Vans says he wrote his book trying to give a "professional account" of what happened, and said that this was his "duty" to do so.
The disappearance of the flight MH370 has triggered a series of theories after it disappeared in March 2014 on a route to Beijing from Kuala Lumpur with 227 passengers and 12 crew members.
The theme of popular theory is government secrecy, and many of them suggest that the only explanation is that the CIA, Russians, Chinese or Malay are responsible for the real reason for the flight to disappear.
Malaysia's current Prime Minister Mahathir Mohamad has confirmed this theory, stating that American secret agents know where the aircraft is.
He said in 2014: "Someone is hiding."
Another theory is battery explosion or mechanical failure.
The cargo holds more than two tons of lithium-ion batteries and more than four tons of mangosteen fruit.
Some are afraid that the fruit juices have leaked and come into contact with the batteries, causing an explosion.
One widely-spread theory is the air pressure in the cabin without pressure, and life-saving oxygen masks did not work.
At 35,000 cubic meters, those on board would only spend 30 and 60 seconds before they took it.
This theory could explain why no distress signals were made from the cockpit or passengers.
The MH370 pilot was the last voice he heard before the plane disappeared, leaving some to think that he was guilty.
Captain Zaharie Ahmad Shah honors Kuala Lumpur airspace, saying, "Hello Malaysia, three seven zero."
Two minutes later, the airplane tracking system was turned off, and some of them had bound their luck to disappear.
Their investigators deny this theory.