The 14-seater aircraft with four crew members en route from Liberia to Mexico touched down at the Freetown International Airport in Lungu, Sierra Leone on September 20.
Authorities say the plane lacked proper landing permits and did not originate from any recognised airfield in Liberia.
It was also operating under a fake registration number and had parts of it scratched off.
Crew members were also found to be three Mexican nationals and a Spanish national after investigations.
The crew claimed a radio failure before landing but a technical inspection revealed otherwise.
The flight captain, who initially said he couldn’t speak English, later confessed to being paid $20,000 to fly the plane.
Investigations are underway by the Sierra Leone Civil Aviation Authority (SLCAA), security forces and the Office of the National Security.
So far, six individuals including two Sierra Leonean air traffic controllers are being investigated.
Local reports indicate that the aircraft has been secured and declared safe with no suspicious items found on board. Sierra Leonean police and military personnel are currently guarding the aircraft while investigations continue.