Buenos Aires — Marcelo Carlos Dupont, a well-liked advertising executive from a respected Argentine family, vanished from Buenos Aires at about 6:30 p.m. last Sept. 30.
Seven days later, his body was found on a sidewalk in suburban San Martin de Tours. The site is 50 yards from an Argentine Army arsenal and in full view of two observation towers at the facility.
That is what the police said at first. Nelson Horacio Corgo, chief detective of the Buenos Aires police homicide division, told reporters flatly: ''It is an open-and-shut homicide case.''
But now, two months later, there is increasing evidence that Marcelo Dupont may have been another victim of the reign of terror that has stalked Argentina since the military came to power in 1976.
Detective Corgo admits, ''There is more to this case than we originally thought.''
The Argentine press is reporting developments in this case - and other new evidence of human-rights abuses in Argentina - with a forthrightness that has not been seen since the military seized power in 1976.
Until now, a wall of silence has surrounded the disappearances of thousands of Argentines during the military's reign. Discovery of the unmarked graves near Buenos Aires, bodies of missing victims in the graves, and an intensifying press spotlight on the issue have breached that wall of silence.
The case of Mr. Dupont, because he was so well known, is a big factor in drawing public attention to the issue of human rights abuse. Journalists here follow his case and the issue of the unmarked graves on a daily basis. Some newspapers, La Nacion in particular, are even trying to uncover facts about the Dupont case ahead of the police.
For its part, the Dupont family - which has played important roles in government, business, and the professions for more than 50 years - has been sure all along that there was more than met the eye to Marcelo Dupont's death. Gregorio Dupont, the victim's brother and a former diplomat, is convinced his brother's assassins were part of the same military apparatus that killed two Argentine diplomats in 1977.
Both Gregorio Dupont and human-rights activists here claim a secret police mafia, operating with the full knowledge of the military and perhaps sanctioned by the Navy, is responsible. Some think former junta member Rear Adm. Emilio Eduardo Massera may have approved of the execution.
''Marcelo's killing was the direct result of statements I made,'' Gregorio Dupont said. ''Directly or indirectly I hold Massera to be responsible for my brother's death.''
It is not overlooked here that just before Marcelo Dupont's disappearance, Gregorio Dupont testified in court on the death of Elena Homberg, an Argentine diplomat who disappeared in 1977. She told Mr. Dupont only days before her death that she ''knew for a fact'' that Admiral Massera had met in Paris with exiled Montonero guerrilla leaders. Some here suspect Massera also is linked with the 1977 abduction of former Argentine ambassador to Venezuela Hector Hidalgo Sola.
The Dupont, Holmberg, and Sola cases, are, in the view of human-rights activists here, merely the tip of the iceberg - ''the spectacular ones that make the headlines,'' as one rights' spokesman says.
Human-rights groups say at least 6,000 Argentines, and more likely thousands more, were killed in the so-called ''dirty war'' that followed the military seizure of power.
The recent discoveries of unmarked graves, including some near the Campo de Mayo military barracks, have focused public attention on the issue. Some victims of torture who escaped their captors say the military took them to the Campo de Mayo facility.
The circumstances of Dupont's death - at first it was thought he died in a four-story fall - are being questioned anew since the press discovered there was no mark of impact on the spot where the body was said to have fallen.
But courts also have acted quickly. Judge Eduardo Ruiz Gerome, who has received death threats in connection with the Dupont case, recently ordered Mr. Dupont's body exhumed for further autopsy.
A new autopsy establishes that Dupont was tortured with electric shocks and other implements before his death.
The case has numerous strange twists. Someone resembling Mr. Dupont, if not Mr. Dupont himself, took a 4,320 kilometer journey, partly by bus, from Argentina through Uruguay to Sao Paulo, Brazil, and back to Argentina during part of the time Mr. Dupont was missing.
Witnesses who saw the traveler in Uruguay and Brazil have been brought here to testify before Judge Gerome. And persons who allegedly traveled on the same buses as Dupont and who have pocketed scraps from their trip that allegedly link Dupont with the bus trip are also scheduled to testify before Judge Gerome. Yet other pieces of paper suggest a Dupont look-alike made the bus trip.
Navy spokesmen, meanwhile, have jumped into the fray. They claim that the torture of Dupont, if indeed it occurred, took place in Brazil, not Argentina. They are circulating a story that Dupont's business was in bankruptcy and that he probably killed himself.
It is a fact that Dupont's company was in financial trouble, but so are about half the companies in Argentina. And autopsies appear to refute that death was a suicide.
As the Dupont case develops, it is startling Argentina. Newspapers have refrained so far from drawing editorial conclusions on the case. The military bars radio and television from mentioning it. But the issue is proving to be damaging to military prestige.
Although the Dupont case is only the latest in a long list of unexplained disappearances and deaths in Argentina, it could prove the catalyst that finally brings the issue to the surface and ferrets out the culprits.
''That, of course, is my hope,'' says Gregorio Dupont.
''It will never bring back Marcelo Dupont,'' says a human-rights activist here, ''but we may finally rid this nation of this evil which has so eaten into the fabric of our society.''