The first-ever archaeological excavations at the Nazi death camp Treblinka have revealed new mass graves, as well as the first physical evidence that this camp held gas chambers, where thousands of Jews died.

Presented in a new documentary, "Treblinka: Hitler's Killing Machine," which will air Saturday (March 29) on the Smithsonian Channel, the excavations reveal that the Nazis weren't as adept at covering up their crimes as they believed when they razed the death camp in 1943. Brick walls and foundations from the gas chambers remain, as do massive amounts of human bone, including fragments now eroding out on the forested ground surface.

"For me, that was quite shocking," said project leader Caroline Sturdy Colls, a forensic archaeologist who normally works with police to find modern murder victims. "These artifacts are there, and these human remains are on the surface, and they're not being recorded or recovered."

Treblinka's horror

Of all the atrocities of Hitler's Third Reich, Treblinka is one of the most mind-boggling. Historians estimate that about 900,000 Jews were murdered at this concentration camp in Nazi-occupied Poland over a mere 16 months.

The Nazis began deporting Jews, mostly from the ghettos of Warsaw and Radom, to Treblinka in July 1942. There were two camps. Treblinka I was a forced-labor camp where prisoners were made to manufacture gravel for the Nazi war effort. A little more than a mile (2 kilometers) away was Treblinka II, a horrendously efficient death camp. [7 Absolutely Evil Medical Experiments]

Jews were sent to Treblinka II on trains, told they were simply going to a transit camp before being sent on to a new life in eastern Europe. The deception was elaborate: Nazis erected a fake train station in the remote spot, complete with false ticket-counter and clock.

"There was an orchestra set up near the reception area of the camp to play," Colls told Live Science. "It was run by a famous composer at the time, Artur Gold."

Gold, a Jewish violinist from Warsaw, was kept alive at Treblinka both to entertain the Nazi guards and to run the orchestra. He died at the camp in 1943.

The Jewish deportees were split into two groups, one of men and the other of women and children, and ordered to undress for "delousing." After handing over their valuables and documents, the victims were sent to the gas chambers, which were pumped full of exhaust from tank engines. Within about 20 minutes, some 5,000 people inside would be killed by carbon monoxide poisoning. Corpses were initially buried in mass graves, but later in 1942 and 1943, Jewish slave laborers were forced to reopen the graves and cremate the bodies on enormous pyres.

Hidden atrocities

But because the Nazis razed Treblinka's death camp in 1943, little physical evidence of this genocide remained. What was known about Treblinka came from Nazi confessions and the eyewitness descriptions of very few survivors, most of whom were never allowed near the gas chambers. [Images: Missing Nazi Diary Resurfaces]

But as an archaeologist, Colls knew that "the landscape could never be sanitized in that way," she said. She began assessing Treblinka as an archaeological site in 2007. Her emphasis was on using "non-invasive" archaeological methods, including geophysical surveys of the site and visual inspection.

"What we wanted to do at that stage was to asses what, if anything, survived below ground," Colls said.

Since that time, Colls has also led a lidar survey of the wooded site. Lidar is a method that uses lasers to measure the distance between the ground and the airplane-borne instrument. By scanning the ground with lidar, archaeologists can detect depressions and mounds that might indicate manmade structures. Lidar allows researchers to virtually strip away the vegetation that might obscure these features on the ground.

"What that revealed was the presence of previously unknown mass graves," Colls said.

The suspected mass grave sites were in Treblinka I, the labor camp. The story of the labor camp is less well-known than the story of the death camp, which is now marked by a memorial. But the labor camp was no less brutal, Colls said: Eyewitnesses report seeing men hacked to death alive, and beatings and murder were commonplace. The largest of the mass graves as revealed on lidar was 63 feet by 58 feet in size (19.2 by 17.6 meters).

Indeed, when the archaeology team began digging to confirm the lidar results, they uncovered shoes, ammunition, and bones — including bones with cut marks indicating that the victims had been stabbed or otherwise assaulted.

After digging three small test trenches to confirm each mass grave, Colls and her team reburied the remains. Jewish rabbinical law prohibits the disruption of a gravesite, so the aim was never to disinter the bodies. But placing the bones back in the grave was emotionally difficult, Colls said.

"I think it never actually crossed my mind that it would actually be me who would re-inter the remains," she said. "I think sometimes the hardest thing to do was to actually re-inter the remains, and to backfill the trenches over the gas chamber, for example, because it felt like you were almost putting a lid on it."

Finding the gas chamber

The gas chamber was the subject of the teams' second dig. There were two sets of gas chambers built at Treblinka, the first with a capacity of about 600 people, the second able to hold about 5,000.

Colls and her team conducted four excavations at Treblinka II. The first two revealed a strange find — a fossilized shark tooth, and sand. Evidently, the Nazis dumped sand from a nearby quarry over the remains of the death camp to disguise them.

The second two trenches, however, revealed a brick wall and foundation. The gas chambers were the only brick buildings in the camp, Colls said. The excavations also revealed orange tiles that matched eyewitness descriptions of the floor of the killing chambers. Chillingly, each tile was stamped with a Star of David, likely part of the Nazi subterfuge that the building was a Jewish-style bathhouse.

"Treblinka had never been looked at since the period after the war," Colls said. "And everybody had assumed that because the history books said it was destroyed, it was."

The excavations prove otherwise, she said. Colls is now working on an exhibition of the findings to go on display at Treblinka, as well as a book about the work. There are plans to go back and dig at an execution site near the labor camp to confirm the presence of a mass grave, she said, and there may be more work near the gas chambers.

The hope, Colls said, is to bring the atrocities to light, understand them, and hopefully prevent future genocides. To that end, she says, she channels the emotion of uncovering victims' remains to finding more answers.

"For me, it feels like the Holocaust happened yesterday," she said.

"Treblinka: Hitler's Killing Machine" premiers Saturday, March 29 at 8pm ET/PT on the Smithsonian Channel.

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