Look closely, and you'll see these huge complexes being built.

From the sky, they sort of look like factories or even schools.

But look even closer: this line is one facility's perimeter wall.

And these shadows?

They're cast by the watchtowers along the wall.

This compound isn't a school or a factory.

It's an internment camp.

Inside these camps, the Chinese government is detaining as many as 1 million Uighurs,

China's mostly Muslim minority.

China doesn't want the world to know any of this.

But the story of these camps is also the story of how we know about them - and China's efforts

to cover them up.

As soon as we began to document the re-education centers, there was

Chinese government officials deleting what we were finding.

Uighurs mainly live here, in the Xinjiang province of northwestern China.

That puts them closer to the capitals of Kyrgyzstan and Uzbekistan than to Beijing.

And Uighurs are also closer culturally to those Turkic groups than they are to the Han

Chinese, China's ethnic majority.

The Uighurs speak a Turkic language. Their culture is different.

They have particular styles of music, a whole a whole rich history

that is unique to them.

This is Sigal Samuel, a reporter at Vox.

I've been reporting on the Uighur crisis in China for about a year now.

China has been concerned for decades about the possibility of Uighur separatism.

Uighurs have actually had their own independent nation, two separate times in the last century.

In 1933, they established the Islamic Republic of East Turkistan here in Kashgar.

But it crumbled less than a year later when it was taken over by Chinese forces.

Then, in 1944, the Soviet Union backed the creation of the East Turkestan Republic, based here.

But when China became Communist in 1949, the Soviet Union turned on East Turkestan, and

helped China take it over again.

Part of why the Xinjiang region is so important to China is that it's rich with energy resources.

And as China's economy grew, so did its need for energy.

Today Xinjiang accounts for nearly 40% of China's coal reserves.

And over 20% of the country's oil and gas.

It also accounts for 20% of China's potential for wind energy.

China needs resources, it needs energy.

It needs the geographical location, the area on which Xinjiang sits.

That's where Uighurs are.

That's where they're living.

And so China really wants to have a solid sense of control over that area.

As far back as the 1950s, China saw an opportunity to dilute the influence of the potentially

rebellious Uighurs, and started encouraging the migration of Han Chinese, into Xinjiang.

And it worked.

In 1945, Uighurs made up over 80% of the population, compared to just 6% Han Chinese.

By 2008, Xinjiang was 46% Uighur compared to 39% Han Chinese.

But over the years, as Xinjiang developed economically, Uighurs were left behind,

working mostly low-wage jobs in agriculture while the Han held higher-paying jobs.

Finally, in 2009, a Uighur protest against discrimination at the hands of the Han and

the Chinese government erupted in violence.

“Bloody riots broke out, pitting ethnic Uighur Muslims against the dominant Han Chinese.”

One of the worst riots took place in the provincial capital of Urumqi.

About 200 people were killed and hundreds injured during the unrest.

That was sort of an inflection point.

After that, the Chinese really started to crack down harder on the Uighurs.

And by 2013, Xinjiang had become even more important to China.

The country launched the “Belt and Road” initiative, a trillion-dollar investment in

things like fiber optic cables, train lines, and gas pipelines meant to boost the country's

economic and political influence around the world by making it easier to trade with China.

If you plot these projects on a map you'll see a lot of them pass through Xinjiang, making

the province arguably the most important corridor for the whole project.

China would need to ensure that Xinjiang remained securely in its hands.

The Uighurs came to be perceived and painted more as a threat,

as a separatist threat, as an extremist threat.

In 2016 and 2017, the country enacted a series of “de-extremification” policies aimed

at Muslims, like banning long beards.

And Xinjiang was effectively turned into a hi-tech police state.

So this kind of thing is happening all over the country, but in Xinjiang it's

been just increased by orders of magnitude.

We're talking about Uighurs having to hand over their phones at checkpoints.

We're even talking about QR codes being installed on the outside of their homes.

But the most brutal part of this crackdown was hidden to the world at first.

In this image you see the opening of this facility.

The signage, it says "De-extremification reeducation center."

Around 2017, China started building these internment camps,

these large scale places to detain Uighurs. China says that these camps are

necessary because the Uighurs are a terrorist threat.

A separatist threat.

People who are infected with extremist thinking.

But it wasn't until Uighurs who had been detained told their stories, that the picture

from inside the camps came into clearer focus.

They're forced to memorize and recite Communist Party propaganda every day.

They're often forced to criticize their own Islamic beliefs and to criticize the beliefs

of their fellow detainees.

“We had to sing songs hailing the Communist Party.

We had to repeat in Chinese, 'long live [Chinese president] Xi Jinping!

There have been reports of death, of torture.

“Three guards surrounded me and abused me.

"Each time I was electrocuted, my whole body would shake."

So there's this atmosphere of just trying to uproot what you believe in.

At first, China denied the existence of these camps...

But activists and academics fought back.

A lot of people around the world

are scouring the Internet for evidence

of China's internment camps for Uighurs.

In terms of the strategies and tools that I've used and others have used to uncover

evidence of these camps, it's quite simply a computer and knowledge of Chinese and thinking

about what ways whats words, especially government websites, would use.

People have unearthed government documents...

"And then we had growing visual evidence. We're looking at satellite images."

We could actually trace the creation and expansion of the reeducation camp.

It was a matter of, I think luck or chance

I uncovered this image.

And until then, we didn't have that piece of visual evidence that said this

is what it is.

And this is what the Chinese government's calling it.

Tim isn't alone.

There's a whole network of “web sleuths” around the world using basic internet tools

to document what China doesn't

want the world to see.

And they've gotten China to change their story, at least a little.

China was denying that these re education centers exist, until journalists

and academics and others started to really amass a body of evidence that was so convincing

that China couldn't just deny it anymore.

China took a different approach and started admitting that these facilities exist, but

carefully painted them as training schools for potential criminals or terrorists.

In the meantime, the camps are still there and growing.

This camp, one of China's largest, was as big as the nearby city of Dabancheng in 2017.

But by 2018, the camp had expanded to twice the size.

From China's perspective they think it's worth it. They want to make sure Xinjiang is an

area of the country that they have total control over.

And if that comes with a high human cost and even a reputational blow on the international

stage, China so far seems willing to do that anyway.