It began as a bank robbery, the biggest in Chile's history, and at first it seemed as plain as it did audacious. Last March 9, in the cold desert country of the north, a bank guard and cashier disappeared into the night with $1.15 million worth of Chilean pesos -- a haul so big that police figured the bills alone had to weigh at least 176 pounds.

In a country such as Chile, where the police make a habit of stopping cars and travelers to examine their documents, two young bank employes spiriting that kind of money around should have been fairly easy to trace. But they vanished, leaving bewildered families and the growing suspicion that there was something very strange about this heist.

There was. On June 12, it was officially announced that police had found the real thieves and wrung from them full confessions of their gruesome crime. Their names were Eduardo Villanueva and Gabriel Hernandez. They had confessed, the announcements said, to abducting the bank employes into the desert, shooting them both to death, blowing up their bodies with dynamite and burying the largest corpse fragments in the deep dry sand.

Both Hernandez and Villanueva were full-time employes of CNI, the National Information Center, the secret police Chile set up after disbanding DINA, the former intelligence service that ordered the 1976 bombing assassination of diplomat Orlando Letelier. Never had the national public image of CNI been so badly shaken -- and the remarkable events that followed only managed to make things worse.

Villanueva, a young man with an apparently shady past and a reputation for tipping flamboyantly in local nightspots, was a CNI agent. Hernandez, a father of three, described in news reports as "serious and responsible," was CNI chief for Calama, where the bank was robbed.

El Mercurio, one of the morning Santiago newspaper, carried reports of investigations records describing the questioning of Villanueva.

Why did you kill them?

"Because my superior told me to."

How far away were you when you shot them?

"A good three meters [three yards], pointing straight at the heads. I wanted to eliminate them quickly."

How good could your aim have been from three meters while firing at night?

"I'm a very good shot. I can fire point-blank from 20 yards, more if I want."

Did you realize what you had done?

"I only knew I had to obey my superior Hernandez . . . Everything was completely quiet until we reached the place where it happened. There we put them both face down. First I shot directly at the head of the guard. Then I got closer and pointed at the cashier. He pleaded with me not to do it. All he said was 'please, don't kill me.' Then he started praying, and I gave it to him.My superior said, 'They have got to be eliminated.'"

As soon as the confessions went public, CNI officials fired both men and handed them over to the courts, adding that they were criminal scum who deserved the strongest possible sentence. "In no way do two people like these reflect on the responsibility and absolute seriousness that characterize the rest of CNI's in Africa, up near the Peruvian border, was somehow involved in the murders as well. Then on June 15 police found a red Mazda parked in the desert south of Arica. Inside, sprawled over the front seats with a bullet hole through his right temple, lay Juan Delmas, the head of Africa CNI.The car keys were in the ignition, and a blue parka lay in the back seat. He had been dead four days.

""Suicide," the CNI said. Somebody pointed out that Delmas was left-handed. Somebody else pointed out that the car, which was found in dry desert with a decomposing body in it, was quite clean of any dust. It was also observed that nobody seemed to have been able to locate the bullet that killed Delmas.

Then the body disappeared.

The body was in the morgue refrigerator, and then it was supposed to have been buried in niche No. 8 of the Arica cemetery. Reporters from the local paper went over to the cemetery and noted that niche No. 8 had three impressive wreaths on it, but no coffin. They checked the local funeral homes to see who might have sold a metal coffin suitable for a deteriorating body -- no record of a sale for a Delmas. The judge who was handling the Delmas case allowed reporters two questions: Had he authorized removal of the body to Santiago? "No." Did he know where the body was? "No."

CNI by this time was coming under public attack unprecedented in its five-year history. The secret police force has been accused over the year of arbitrary detentions and of regularly torturing people inside its headquarters. But much of that criticism came from the lone voices of exiles and human rights activists. Now there were lawyers proposing the force he disbanded, mainstream newspapers demanding the agency be more carefully supervised, press conferences bemoaning the idea of a nation fearing its own police.

Delmas, the CNI insisted, committed suicide. They said he shot himself with his right hand because he was ambidextrous with a gun and because it is very hard to shoot yourself with your left hand while sitting in the driver's seat with the window rolled up. They said he was peacefully burried in niche No. 8 of another part of the cemetery, and they said there was no dust on the car because it was in a "crusty area" where the dust does not blow around.

Much of this did not go over too well with the reporters around Africa, who said, for example, that they had photographs of the tracks their own autos and feet had made in the dust near the Mazda. The Arica cemetery owner, who by late late month was becoming somewhat desperate, said the press was driving him crazy and that reporters should get a court order if they want to exhume the body.

In the meantime, four other men have been arrested in connection with the "Calama crimes," as the case is now known in the reams of newsprint it has inspired. One was also a CNI agent. With about $350,000 of the money still missing -- police said part was recovered during their investigation and arrests -- Chilean government and CNI officials are explaining the scandal as a case of "rotten apples" in an otherwise exemplary institution.

The lates twist, which may or may not have anything to do with the Calama crimes, began when Humberto Tapia Barraza, a 60-year-old CNI worker, was shot to death in his doorway as he left for work one morning last week. Tapia was a retired military man, officially working in an administrative desk job. Someone claiming to represent the "popular militia" claimed that Tapia had been killed to avenge a presumed leftist who had been shot to death in an earlier bank holdup.

Two days later, on a deserted Santiago road, police found the body of a young man who had been stabbed to death and left near a piece of carboard on which the letter "R" -- associated with "Resistance," or the Chilean left -- had been drawn in own blood. Another body, bearing machine gun wounds, was found in a separate part of town.

The murders, according to boasting calls to newspapers were the work of the "commando of avengers of Humberto Tapia Barraza."