PHNOM PENH, Cambodia -- In an unkempt courtyard here behind high walls topped by coils of barbed wire lie 14 graves marked only by crude white fences.

They are said to contain the unidentified last victims of Tuol Sleng, a former high school on the outskirts of Phnom Penh that was converted into a prison and death camp from 1975 to 1979 by the communist Khmer Rouge regime then ruling Cambodia.

According to a surviving Tuol Sleng inmate, Ung Pech, at least one American and possibly two may be buried in the courtyard, among the last prisoners killed before invading Vietnamese troops swept into Phnom Penh on Jan. 7, 1979, and drove out the Khmer Rouge forces led by dictator Pol Pot.

Now maintained as a macabre museum in memory of those who died under the Khmer Rouge, Tuol Sleng has been well publicized by the Hanoi-installed government here, which seeks to graphically demonstrate the Pol Pot regime’s brutality and thus justify Vietnam’s continuing occupation of Cambodia. Despite the publicity, however, the circumstances surrounding the disappearances of a dozen Westerners captured by the Khmer Rouge have remained murky.

Although much has already been written about Tuol Sleng, new details of the prison are still emerging as its custodians learn more about what happened there from the voluminous records kept by the Khmer Rouge. These records reveal much about the Khmer Rouge, who virtually closed off Cambodia from the outside world during their four-year rule and who are now waging a guerrilla war from bases in the country’s most remote areas.

Among the foreigners held at Tuol Sleng, according to prison records examined here, were four Americans who disappeared in 1978 while sailing yachts off the coast of Cambodia. They were either tortured to death or massacred, Ung Pech says, along with about 20,000 Cambodians who passed through Tuol Sleng between 1975 and 1979.

Two years ago, when accounts of the horrors at Tuol Sleng began to emerge, the U.S. State Department refused to comment on reports that Americans may have been among the victims, citing U.S. privacy laws. According to the prison documents, however, the four Americans were captured in two groups in April and November 1978 and brought to Tuol Sleng shortly afterward.

The first two caught were James William Clark of Anaheim, Calif., and Lance McNamara of Santa Barbara, whose boat was fired on and captured by a Cambodian vessel. Seven months later, Michael Scott Deeds of Long Beach, Calif., and a companion identified as Christopher Edward Delance were sailing near an island 60 miles from the Cambodian port of Kompong Som when their boat was seized, according to the records.

The documents show that Deeds and Delance entered Tuol Sleng on Nov. 26, 1978, a month before the Vietnamese invasion that eventually overthrew Pol Pot. Their “confessions,” translated into the Khmer language, are dated Jan. 5, 1979, two days before the Vietnamese captured Phnom Penh.

When the Vietnamese entered Tuol Sleng on Jan. 7, they found the bodies of 14 persons killed shortly before the Khmer Rouge guards fled the prison.

Several photographs taken by the Vietnamese and now on display at Tuol Sleng show the grisly scenes they discovered in former classrooms-turned-torture chambers: bodies manacled hand and foot to metal beds; heads battered into pulps with a variety of implements including iron bars, axes, shovels and garden hoes; floors stained by pools of blood and littered with torture instruments such as whips, bamboo sticks and lengths of electric wire.

Other rooms in the complex of three-story school buildings contain more torture tools, including instruments for pulling out fingernails, vats for drowning prisoners and devices for administering electric shocks. Outside, in the courtyard near the 14 graves, stands a gallows-like contraption used for suspending prisoners by arms bound behind their backs or for dunking them in large pots of water.

Many times, Ung Pech says, he heard the voice of an American screaming in pain, calling for his mother or father and begging for the torture to stop.

“There were terrible cries,” Ung Pech said, “especially at night.”

The tortures of both foreigners and Cambodians were usually aimed at extracting confessions of complicity with the U.S. Central Intelligence Agency, or sometimes the Soviet KGB, according to Ung Pech, who is now a director of the Tuol Sleng museum.

Arrested in 1977 and subsequently tortured himself -- two of his fingernails are missing -- Ung Pech was spared because of his skill in maintaining the prison’s electrical generating equipment, he said. Other survivors included an artist who painted oil portraits of Pol Pot, a sculptor who turned out busts of him and one prisoner who escaped while being driven to a site for mass executions, Ung Pech said.

Like the foreigners’ confessions, those extracted from the Cambodian prisoners are replete with “admissions” of far-fetched CIA activities, sometimes going back for decades. A majority of the Cambodians held at Tuol Sleng were themselves Khmer Rouge members who, along with their families, became the victims of successive purges.

Some of the admissions extracted at Tuol Sleng appear ludicrous. For example, Delance’s confession gives his “working CIA code number” as 570-80-677 -- clearly a Social Security number.

While Delance and Deeds apparently were massacred shortly before the end of Pol Pot’s four years of brutal rule, Ung Pech believes at least one of the other Americans, James Clark, may have died under torture. The former Cambodian prisoner, one of only a dozen persons to survive Tuol Sleng, thinks both Clark and McNamara died in late May 1978, little more than a month after they were captured.

In a 20-page typewritten confession dated May 23, 1978, Clark spins a bizarre tale of drug smuggling as a cover for CIA espionage over a three-year period. The paper, evidently typed by Clark himself, describes contacts with a variety of alleged CIA accomplices and travels that took him to Mexico, Europe, North Africa and Southeast Asia.

In several places in the account, Clark obviously is telling his Cambodian jailers what they want to hear, giving details of his alleged CIA links that sound odd to an American reader. In relating his recruitment by the CIA, for example, he writes, “I signed a receipt paper which made me a member of the CIA with the number 1492.”

Describing the origins of what he called his Cambodian “intelligence mission,” Clark said he was commissioned by a man named Henderson in July 1977 to photograph fishing boats, warships, islands and radio or radar installations off the coast of Cambodia.

“This was because Cambodia was a very new but powerful country that seemed to be getting stronger each year,” Clark wrote. He also called Cambodia “the most successful communist country.”

Clark said he and McNamara left the port of Pattaya, Thailand around midnight April 18, 1978, and sailed toward Cambodia, sighting an island two days later and photographing it from a distance. Then, he wrote, a Cambodian gunboat approached. Clark described it as a converted wooden fishing boat armed with a 20mm cannon and a machine gun.

He said that when his boat came under rifle fire, “I thought this was a pirate boat and fired about 15 rounds from my revolver and Lance’s automatic, hoping they might go away.”

Clark continued, “The Cambodian boat shot at us with the 20mm cannon and my boat was hit. I stopped, and the Cambodian forces caught me.”

That, he wrote, ended his “intelligence mission,” for which he said he was to receive $700,000 and McNamara $400,000. “As to Cambodia,” he concluded, “the CIA will keep on bringing its agents of all kinds to spy upon it.”

A copy of the last page of Clark’s confession is displayed on a wall in Tuol Sleng below a photograph showing a handsome man with bushy dark hair and regular, clean-shaven features. On another wall in another room, a different photograph catches the eye. It shows, from the bridge of the nose on down, the emaciated body of a man with a black beard, pale skin and broad shoulders. The facial features discernible resemble those in the picture above the page from Clark’s confession.

The photograph is among scores of pictures taken by the Khmer Rouge of prisoners who died under torture. Saved by the former prison authorities as part of their meticulous record-keeping, the photos now illustrate the legacy of Pol Pot’s Cambodia, a regime that the current government calls the most murderous since Hitler’s Germany.

Despite the gruesome nature of the exhibits, which were arranged with the help of Vietnamese and Soviet advisers, Tuol Sleng continues to fascinate. Every Sunday, when it is open to the public, 2,000 to 3,000 Cambodians come to tour the prison, according to director Ung Pech.

They view the torture chambers and file through classrooms in which small 6-by-4 foot brick cells were built to hold prisoners. But mostly they peer at the thousands of pictures that line the walls, looking for friends and relatives among the faces of Cambodians photographed on the day of their entry into Tuol Sleng.

They are faces from many walks of life: former government and Army officials, teachers, doctors, engineers, workers. Most are men, but there are many women. Some of the faces are of children under 12. A few are of infants. Many of the faces plainly show terror. Some betray hatred of their captors. And others look dazed and bruised.

On some of the pictures, visitors have written a few words in Khmer to identify the victims. One such photograph shows Hing Sokhom, a Cambodian professor who returned to his country from New York to lend his support after the Khmer Rouge took power, only to be jailed and killed for his trouble.

A strikingly pretty face belongs to actress Marina Kiriwat, the daughter of Cambodia’s former U.N. ambassador, Hout Sambath, according to a guide.

As visitors move through room after room of photographs and other exhibits, they can trace the growing paranoia of the Khmer Rouge revolution as it began to increasingly turn inward and feed upon itself. Most of the photographs dating from the bloodiest months of the regime in 1978 are of Khmer Rouge soldiers, cadres, provincial officials and even Tuol Sleng guards and interrogators arrested on suspicion of being traitors or CIA agents.

A guide at Tuol Sleng, Chey Sopheara, points to the photograph of a man identified as a Khmer Rouge province chief and announces, “that was the man who killed my father.” The official was arrested during a purge in 1978, Sopheara says with satisfaction. “So I got my revenge.”

While many inmates died in Tuol Sleng, most were held for a while at the prison, then driven to sites outside the city and killed with axes, sledgehammers, picks, shovels and other implements. A case at Tuol Sleng contains some of these tools, many still stained with blood, and mass graves dug up after the Khmer Rouge were driven from power provide further evidence of these massacres.

But perhaps the most haunting of the displays at Tuol Sleng is a wall covered with the photographs of healthy looking youths, some apparently no more than 13 or 14 years old.

These are the faces of the Khmer Rouge. Mostly poor peasant boys recruited in their teens to fight against the former U.S.-backed government of Lon Nol, they were trained to hate and kill their enemies. After the Khmer Rouge victory, they became the guards, torturers and executioners of Tuol Sleng.

Most of them -- more than 200, according to Ung Pech -- escaped just before the first Vietnamese troops drove into Phnom Penh. Now they again form part of a Khmer Rouge force fighting to take power in Cambodia.

With them in the jungles of western Cambodia, according to officials here, is Kaing Kek Iev, the Khmer Rouge security chief formerly in charge of Tuol Sleng. Having risen even higher in the Khmer Rouge hierarchy since then, he is reportedly one of Pol Pot’s right-hand men.