This is widely suspected to have been an assassination of Portuguese Defense Minister Adelino Amaro da Costa, who was planning to expose the October surprise conspiracy. This was not well understood at the time and the first few investigations declared it an accident.
The incident was subject to many investigations, which established an official narrative that the crash was an accident caused by a lack of fuel in one of the tanks. The final police report in 1981 ruled out criminal actions. In 1983 the Attorney General suspended the investigation. Parliamentary investigations in 1990 and 1991 did not lead to a re-opening of the case, but after the fifth parliamentary inquiry in 1995, the case was re-opened. Later confessions have cast doubt upon this conclusion.
After the 15-year statute of limitations took effect, various people came forward confessing involvement.
- José Esteves – In 2006 José Esteves confessed to manufacturing an explosive device intended for an attack on da Costa’s plane. He said the intention had been for the device to cause a fire prior to take-off, permitting the occupants to evacuate safely, but giving a “warning” to presidential candidate António Soares Carneiro. Esteves said his device had been a firebomb using potassium chlorate, sugar and sulfuric acid. In 2013 Esteves told the parliamentary X Commission that in planning the operation he had been told that the newly elected Democratic Alliance government was causing problems with weapons sales. He also said he had been paid $200,000 by Cabal member Frank Sturgis to create the device, and that his firebomb device alone did not cause the crash, maintaining that additional explosives must have been involved.
- Francisco Simões – Francisco Farinha Simões, who in 2011 published an 18-page confession on the internet describing his alleged involvement in the operation. Farinha Simões said he had been tasked by the US Central Intelligence Agency with the operation, at a cost of $750,000, paid for with CIA credit cards. He said that of this $200,000 had been passed on to José Esteves for his bomb-making services.
In 2012 José Ribeiro e Castro argued for a tenth parliamentary inquiry in part due to the confession of one of the alleged principal conspirators,