It is very likely that Avianca 203 was not destroyed by a bomb but rather by a fuel system explosion of the type that destroyed at least five other Boeing aircraft, and which led to numerous Airworthiness Directives by the FAA, culminating with the mandatory installation of nitrogen inerting systems in the fuel tanks of 727 and 737 aircraft.
A great deal of false information has been propagated about Avianca 203. The Colombian newspaper El Espectador has recently published an eight part report reviewing the known facts of the disaster and questioning whether there is any competent evidence that a bomb was involved. The articles can be found at www.elespectador.com/files/especiales/a ... index.html
. The articles are written in Spanish. The El Espectador articles raise several main points. 1. There was never a competent and complete accident investigation of Avianca 203. Although the plane fell on land, near the city, much of the debris was never recovered or examined, and left in the field or carried off by thieves. No bomb parts or pieces were recovered, at the crash site, or in subsequent studies of recovered parts. 2. The only "evidence" of a bomb was the opinion of an FBI agent, whose opinion was subsequently officially discredited in the FBI "Labgate" scandal which emerged in 1996. The opinion of the FBI agent was based on his physical observation, which lacked any scientific basis, and certain lab results which were obtained in the FBI laboratory which could not, however, rule out the possibility of contamination of the examined samples. 3. It is impossible to say how many people were aboard the flight or who they were. 4. There was a history of mechanical problems with the 727 aircraft which exploded. A circuit breaker serving the right wing boost fuel pump had ripped ten times in the two months before the accident, and been reset by Avianca maintenance personel without the discovery of any cause of the breaker trip. In the other Boeing aircraft fuel system explosions, the fuel pumps and the wiring serving the fuel pumps were found to be the likely causes of the explosions. All eight of the fuel tank boost pumps were removed from the crash scene by unknown persons, and therefore could not be examined. Therefore, it is very difficult to rule out a similar fuel system cause for the explosion of Avianca 203 based on the available remaining evidence.
Over the years, a number of different "confessors" have come forward and claimed to have inside knowledge that a bomb was planted on the flight. These individuals are mostly mafia and ex-mafia members who have offered "information" to aid their own criminal cases. As these stories have emerged over the years, the "explanation" of Avianca 203 has evolved, changed, and taken on many bizarre features, including the "Gaviria" story to which you refer, and several other scenarios, including the alleged use of a tape recorder, etc. None of these stories is supported by independent evidence. For example, Gaviria himself has pointed out that in 1989, when he was a presidential candidate, he did not travel on regular commercial flights and never planned to travel on Avianca 203 or any other Avianca flight.
The known sequence of events in Avianca 203 was extraordinarily similar to the sequence of events established in TWA 800, a similarity which is noted in the accident report of TWA 800. TWA 800 was officially attributed to a fuel system explosion, after a great deal of careful scientific investigation. The other four known Boeing fuel system explosions (all of which happened in aircraft which were parked on the tarmac at the time of explosion) all demonstrated features similar to Avianca 203, that is, a smaller initial explosion, followed by a short period of fire, followed by a second much larger explosion which destroyed the aircraft. In every one of those cases, the probable cause of the accident was found to be, after careful investigation, a fuel system explosion initiated by electrical malfunctions.
If you are interested in Avianca 203 I suggest that you find and read the El ESpectador series, which contains a great deal more information than can be presented in this format.