United Nations human rights chief Navi Pillay is in charge of global investigations. She is a thug herself as she is more concerned with charging Edward Snowden or Israel for their defense mission against the terror organization, Hamas.

So then why would al Assad of Syria get a pass on torture? Evil IS the United Nations.

10,000 Bodies: Inside Syrian President Bashar al-Assad’s Crackdown

Photographs of Corpses Offer Evidence of Industrial-Scale Campaign Against Political Opponents by Assad Regime, U.S. Investigators Say

At Hospital 601, not far from the presidential palace in Damascus, Syrian guards ran out of space to store the dead and had to use an adjoining warehouse where military vehicles were repaired.

A forensic photographer working for Syria’s military police walked the rows and took pictures of the emaciated and disfigured corpses, most believed to be anti-Assad activists. Numbers written on the bodies and on white cards, the photographer said, told regime bureaucrats the identities of the deceased, when they died and which branch of the Syrian security services had held them. (Graphic image follows.)

U.S. investigators who have reviewed many of the photos say they believe at least 10,000 corpses were cataloged this way between 2011 and mid-2013. Investigators believe they weren’t victims of regular warfare but of torture, and that the bodies were brought to the hospital from the Assad regime’s sprawling network of prisons. They were told some appeared to have died on site.

Last year, the Syrian military-police photographer defected to the West. Investigators later gave him the code name Caesar to disguise his identity. He turned over to U.S. law-enforcement agencies earlier this year a vast trove of postmortem photographs from Hospital 601 that he and other military photographers took over the two-year period, which he helped smuggle out of the country on digital thumb drives.

Over the ensuing months, U.S. investigators pored over the photos, which depicted the deaths and the elaborate counting system, and started to debrief Caesar and other activists involved in his defection. U.S. and European investigators have since concluded not only that the images were genuine, but that they offered the best evidence to date of an industrial-scale campaign by the government of Bashar al-Assad against its political opponents. U.S. Ambassador-at-large Stephen Rapp, head of the State Department’s Office of Global Criminal Justice, has compared the pattern to some of the most notorious acts of mass murder of the past century.

This account, based on interviews with war-crimes investigators in the U.S. and Europe, more than a dozen defectors, and opposition leaders working with Caesar, provides fresh details about Syria’s crackdown on its political opponents and the central role of Hospital 601 in processing bodies and documenting the deaths for the government.

Investigators haven’t finished analyzing the entire cache of photographs and are still trying to gather evidence to fully understand the regime’s role in the deaths. Prosecutors must be careful about jumping to conclusions before all the evidence is in, cautioned a senior U.S. official, who noted that investigators are far from finished debriefing Caesar.

The Federal Bureau of Investigation unit that investigates genocide and war crimes, and other agencies, hope to soon get a more detailed account of what happened at Hospital 601 from Caesar, officials said. Some U.S. officials want to use Caesar’s photographs, which show bodies that appear to have been strangled, beaten or disfigured, to build a case for a potential war-crimes prosecution of the Assad regime. It is unclear when, if ever, such a case might be brought.

When the issue was debated in the White House in 2012 and 2013, many administration officials argued that a concerted push for an international war-crimes prosecution would undermine any chance for pursuing a negotiated settlement to Syria’s civil war, according to participants. Bringing an indictment would give Mr. Assad and his backers little incentive to back down, they said.

“For the administration, it is a double-edged sword,” said Frederic Hof, who served as a top Obama administration adviser on Syria, of the photographic evidence. “On the one hand, it’s going to illustrate perhaps better than anything heretofore the absolute horror of what’s going on. On the other side, it raises the inevitable question: What are we actually doing about it?”

Numbers written on the bodies and on white cards told regime bureaucrats the identities of the deceased, when they died and which branch of Syrian authorities had held them, according to a Syrian military-police photographer now outside of Syria. Faces have been obscured at photo source’s request.

A White House official said the administration has long supported efforts to gather evidence of international crimes in Syria and earlier this year backed a United Nations Security Council resolution to refer war-crimes allegations to the International Criminal Court in The Hague. That resolution was vetoed by Russia and China.

Syria has dismissed Caesar’s photographs as fabrications. In January, before U.S. investigators judged the photos authentic, Syria’s Ministry of Justice said many of the dead shown in the photos were civilians and soldiers killed by “terrorist groups.” It branded Caesar a fugitive lacking credibility, and said the photo trove was part of a campaign instigated by enemies of the nation. Syrian officials at the U.N. didn’t respond to requests for further comment.

Caesar, a high-school dropout from Damascus who has told U.S. officials he is in his 40s, was conscripted into the Syrian military, where he specialized in crime-scene photography. He told investigators he eventually became head of the division that photographed bodies for government records. It was part of Syria’s system, similar to those run by governments around the world, to document civilian and military deaths.

Caesar and the other photographers on his team were stationed at the military-police headquarters in Damascus, he told investigators. In more peaceful times, he was accompanied by a doctor and by a member of the Syrian judiciary whenever he went to take pictures of crime scenes and accidents.

“We had this routine,” Caesar said, according to a person present at his questioning. “As the revolution started out, we continued that same routine.” It was the body count and the venues that changed.

Initially, the Syrian government took many of the bodies of activists to a military hospital in Damascus known as Tishreen, or 607, he told investigators. Tishreen also was the site of military funerals for top Syrian officers, according to activists working with Caesar. Because the military didn’t want the bodies of activists and officers taken to the same facility, it decided to make 601 the central collection point for activists’ bodies, according to investigators who debriefed Caesar.

As the government stepped up its crackdown, Caesar told investigators, he and his team snapped pictures of between 15 and 20 bodies a day. In those early months, bodies were identified by name, he said.

Bodies were brought to 601 from 24 Syrian prisons and laid out in what Caesar and activists described to investigators as the hospital’s auto-repair warehouse.

It isn’t clear from the photos where the people were killed. U.S. investigators believe most died at government detention facilities because they appeared to have been dead for hours or days. A series of photographs taken on Nov. 1, 2012, show a prisoner, apparently alive, grasping a gloved hand before later turning up dead, according to officials who reviewed Caesar’s archive.

Caesar told investigators he didn’t have political affiliations and that before the war he never thought much about his job snapping pictures of the dead. “It was his day job,” said an activist who helped him escape. “He did what he was ordered to do.”

But as the bodies piled up and evidence of torture became more pronounced, Caesar’s attitude began to change. He confided in a close relative who knew activists working with the opposition, and in the summer of 2011 Caesar agreed to start smuggling photographs out of the hospital.

Caesar downloaded the images onto a government computer at his office and stored them on thumb drives that he hid in his shoes and passed to the opposition, Caesar and defectors working with him told investigators.

In October 2011, with the death toll in the prison system rising, the Syrian government introduced a numerical system to track the dead, according to Caesar’s account. Earlier pictures showed bodies marked with names. New ones showed numbers.

The numbers—written on white cards and taped to the bodies, or written directly on foreheads, arms and chests—provided a running count of how many had been killed, U.S. investigators believe.

Cherif Bassiouni, who chaired several United Nations war-crimes investigation commissions and teaches at DePaul University, reviewed Caesar’s photographs on behalf of the Syrian opposition and studied Syria’s use of numbers to identify bodies. He said the record-keeping system bore similarities to the method used by Soviet intelligence services in the 1950s.

Mr. Bassiouni said the Syrian government, like the Soviets, assigned prisoners a unique number when they were alive and a separate one when they died. In Nazi Germany, prisoners received only one number, which stayed with them in life and in death, he said.

The system appeared designed to maintain internal military discipline and track which branch of the military did what, Mr. Bassiouni said.

Last year, Syrian officers added two Arabic letters into the numeric system to indicate when the body count had surpassed 5,000 and 10,000, investigators concluded based on Caesar’s account and an analysis of the photos. It may have been a way to disguise the scale of the killing to anyone who doesn’t know how the record-keeping works, Mr. Bassiouni said.

The State Department’s Mr. Rapp has said the Syrian system stood out from recent mass killings in Rwanda and Liberia because of the level of documentation.

Defectors, former patients and local residents said 601 also functioned as a hospital for sick prisoners. Before a prisoner would be sent to 601, guards would write a number on his or her forehead, according to two Hospital 601 detainees who were there at different times in 2013.

“Forget your name. You’re now this number,” one former prisoner now living in Europe recalled being told by a guard.

The former prisoner, Mazen Besais Hamada, said he was blindfolded and loaded onto an ambulance in January 2013 for the drive to the hospital from the detention center where he was held. Mr. Hamada said he was given the number 1,858.

Conditions inside the hospital were gruesome, according to survivor accounts and witness reports compiled by Syrian human-rights groups, including the Violations Documentation Center in Syria, which is now based in Turkey.

“If you were at a demonstration, you would prefer to be shot and killed instead of shot and injured and taken to 601,” said Qutaiba Idlbi, a 24-year-old Syrian activist who said he was twice arrested and tortured by the regime before fleeing to the U.S. and seeking asylum.

Both Mr. Hamada and another former patient at the hospital described beds containing as many as four prisoners. They said they had to step over dead bodies in the morning to use the bathroom, where guards temporarily stored the corpses. Mr. Hamada said he eventually was freed by a judge.

A former surgeon at the Tishreen military hospital, where activists’ bodies initially were sent, said in an interview that doctors weren’t allowed to know patients’ names—only the numbers they were assigned—because the regime was concerned doctors might recognize a family name and reach out to relatives. The doctor said when a patient died, the family name was disclosed so the doctor could prepare a death certificate. He said the doctors were required to cite “a heart attack, a stroke, a normal medical reason,” even if they knew the cause of death was torture.

The doctor’s account of preparing misleading death certificates is consistent with information collected by activists.

By 2013, Caesar’s team was photographing between 50 and 60 bodies a day at 601, he told investigators.

Caesar began to worry when his bosses at military-police headquarters told him they wanted him to start training another photographer to take over his slot, according to activists working with him. Caesar started to suspect that the regime was on to him.

Last summer, shortly before a chemical-weapons attack attributed by Western nations to the Assad regime killed upward of 1,400 Damascus residents, Caesar told opposition contacts he wanted to leave the country. Syria has denied responsibility for the chemical attack.

To throw off the regime while Caesar was smuggled out of the country, the opposition Free Syrian Army faked the photographer’s death, according to David Crane, a former war-crimes prosecutor who has interviewed Caesar, and activists who were involved.

All told, Caesar helped smuggle more than 50,000 pictures out of Syria—his own and many others he downloaded that were taken by other photographers, according to activists working with him.

Working through the images, some of which show the same bodies from different angles, activists have identified around 6,700 individual victims so far. A senior U.S. official said the numbering system shown in the photos “is consistent with there being more than 10,000 victims.”

In January, a six-member international team of experts interviewed Caesar and examined the photos for any signs they were faked to discredit the Syrian regime. In a report presented to the U.N., the group concluded the photos were genuine.

The senior U.S. official said a separate American analysis of around 27,000 of the images turned up “no evidence of forgery or falsification in the pictures themselves.” The U.S. and other Western governments are expecting to see another 25,000 photos.

Mr. Crane, a member of the legal team that scrutinized the photos presented to the U.N., said “the last time we saw this kind of bureaucratic processing of humans was at Nuremberg.”

—Jess Bravin contributed to this article.

Write to Adam Entous at [email protected] and Dion Nissenbaum at [email protected]