Underwater video footage shows one occupant visible in the wreckage of the plane which was carrying Cardiff City footballer Emiliano Sala, the Air Accidents Investigation Branch said.
In a statement, the AAIB said: "Having identified a priority search area last week, the AAIB agreed a search strategy with Blue Water Recoveries Ltd to maximise the chance of locating the aircraft wreckage.
"The AAIB commissioned specialist vessel Geo Ocean III and Blue Water Recoveries Ltd commissioned FPV Morven and the search area was divided between the vessels. Both vessels began their search on the morning of Sunday 3 February.
"Early in the search, the Morven identified an object of interest on the seabed using its side-scan sonar equipment. It cleared the immediate area for the Geo Ocean III to use its underwater remotely operated vehicle (ROV) to survey the area of the seabed in which the object was located. Based on analysis of ROV video footage, the AAIB investigators on board the vessel concluded that the object is wreckage from the missing Piper Malibu aircraft, registration N264DB.
"The ROV carried out a further search of the area overnight, but did not identify any additional pieces of wreckage.
"Tragically, in video footage from the ROV, one occupant is visible amidst the wreckage. The AAIB is now considering the next steps, in consultation with the families of the pilot and passenger, and the police.
"The image shows the rear left side of the fuselage including part of the aircraft registration.
"We intend to publish an interim report within one month of the accident occurring."
Parts of the plane which disappeared with Sala and pilot David Ibbotson on board were found in the English Channel on Sunday.
David Mearns, a marine scientist who directed the private search on behalf of the Sala family located the wreckage just hours after the search began.
Following the discovery, Sala's father described his "desperation" at the news.
The Piper Malibu N264DB carrying 28-year-old Sala and 59-year-old Mr Ibbotson disappeared over the English Channel on January 21 after leaving Nantes in France for Cardiff.
The plane had requested to descend before losing contact with Jersey air traffic control.
An official search operation was called off on January 24.