A photographer who says he worked for the Syrian government arrived in the US earlier this year carrying flash drives filled with gruesome photos.

The photographer, who goes by the name "Caesar," got in touch with the US Holocaust Memorial Museum in Washington. Now the museum has put some of those pictures on public display.

"When we saw the pictures that Caesar had escaped with, when we saw just how horrific the scale and the scope of the killing has been, his story — of being a witness to these crimes and escaping to tell the world what was going on — it really resonated with us as an institution," says Cameron Hudson, the director of the museum's Center for the Prevention of Genocide. "And so we felt an obligation to help tell his story."

The photos, which the Assad regime claims are fake, show dead bodies stacked like cordwood, many of them emaciated and showing signs of torture. Hudson says the museum has relied on independent sources, including the FBI Crime Lab and the US State Department, to verify the authenticity of the images.

He says Caesar, whose own story has been investigated along with his photos, was well-positioned to collect the images: "He was a staff photographer for the Assad regime ... and one day he was sent to a secret detention facility that he didn't know existed, and was instructed to take pictures of corpses that were beginning to pile up."

That was in 2011. Caesar kept shooting as the bodies accumulated and Syria's civil war became more fierce. When he escaped from Syria with the help of opposition forces, Caesar was carrying what Hudson calls a "treasure trove" of 55,000 images reportedly taken by Syrian military police through 2013.

"When you look at the photographs, many of them are annotated with a prisoner number, with a date, with a detention facility name," Hudsaon says. "What you get is the impression that this is a very organized, methodical and systematic campaign," images that are certainly familiar at the museum.

The exhibit, called "Genocide: The Threat Continues," features a slideshow of some of the images smuggled out of Syria by Caesar. Hudson says it complements the museum's permanent collection.

"As people are reflecting on the period of the 1930s and 40s, you know, they're confronted with this imagery and with this warning that the threat of genocide continues today," he says. "I think it's a very powerful continuation of a very sad story that the museum is telling."

Caution: Some of these images are disturbing.