John Greenewald has spent his life trying to pry secrets out of the US government. Now, he’s asking for some help to get his hands on some of the most elusive documents he’s ever tried to nab.

On Wednesday of last week, Greenewald, who runs the declassified-document clearinghouse the Black Vault, started a crowdfunding campaign on GoFundMe to raise money for the fee the Central Intelligence Agency is charging him for his latest Freedom of Information Act (FOIA) request. He’s hunting for documents related to the notorious MKUltra program (often referred to as the CIA's "mind control" project), an endeavour he embarked on after realizing that the agency had left out thousands of pages from a FOIA request Greenewald filed about the program back in 2004.

The fee, based on reproduction costs set at ten cents per page, comes out to $425.80. Greenewald said he was denied a waiver, usually given to members of the media or FOIAs that pass a public-interest test. “There’s really not much I can do besides cut the check,” he told me over the phone.

As of Monday, he’s over halfway toward his fundraising goal, which he set at $500 to account for GoFundMe fees and potential surprise surcharges.

MKUltra was a covert CIA program launched in 1953 to study the effects of drugs and chemicals on human behavior. In particular, American spies were interested in how they could induce states such as hypnosis, amnesia, and even physical paralysis. It was a Cold-War effort to keep up with the Soviets, whom the CIA believed were using such techniques to brainwash Americans. As part of the program, unaware test subjects—often marginalized people like prisoners and sex workers—were dosed with drugs such as LSD and secretly observed.

Read More: The Most Evil Human Trials in the History of Science

At least one death has been attributed to the program: military scientist Frank Olsen, whose drink the agency spiked with LSD at a research conference in 1953. He would later die after a suspicious fall from a Manhattan hotel room, which was the subject of the recent Errol Morris documentary Wormwood.

Greenewald, now 37, was only 15 years old when he sent his first FOIA request, he told me, thereby launching the Black Vault. This was 1996, before the days when a FOIA response could be delivered digitally. He remembers receiving thick paper files in the mail, he told me, and then typing them up by hand—this was before he could afford a scanner.

“To me, even though the government lies, documents do not,” said Greenewald. “And documents tell a very interesting story. That’s why I love them.”

The saga around Greenewald’s quest for the documents started 14 years ago, when he sent his first FOIA request to the CIA regarding MKUltra. He received four CD-ROMs with thousands of pages of documents on them, remnants of what was left after the agency purged most of their records about the program in 1973, and uploaded them to the Black Vault website in 2004. Out of the 2 million pages of declassified documents on the site, the MKUltra archive quickly became the most downloaded, and still is today. Greenewald said the Black Vault gets between 14,000 and 18,000 unique visitors daily.

But in 2016—12 years after the documents went online—Greenewald realized something was missing. According to Greenewald, another researcher on Reddit cross-checked the documents on the CD-ROMs with an accompanying table of contents from the CIA, and found 4,358 pages that were listed in the index but missing from the cache of documents that Greenewald received in response to his FOIA request.

“So I picked up the telephone and called [the CIA],” said Greenewald. “I didn’t know this at the time, but that would start a two-year-plus battle to prove to the CIA that those documents were not on that CD-ROM.”

Read More: The US Army Funded Astral Projection and Hypnosis Research in the 80s

Greenewald said he went back and forth with multiple people from the CIA’s FOIA office, trying to show them that, all those years ago, they hadn’t sent him everything they should have. But he was met with constant roadblocks. “These guys won’t even tell you what their first name is,” said Greenewald. “It made it very problematic to gather up what I needed and get back to them.”

In May, he compiled and sent a 97-page fax as final proof that the documents were not included in the original FOIA, and finally, his work paid off. Sort of.

The CIA employee he was speaking to (again, unwilling to share his name, according to Greenewald) told him that he was right, the 4,358 pages were missing. “At that time, the story changed,” said Greenewald. The employee told Greenewald that those pages were actually never meant to be included in the first place, because they dealt with “behavioral modification,” and not MKUltra, Greenewald told me.

“Whether or not that ties into MKUltra and mind control, which I believe it does, the CIA claims it does not,” said Greenewald. His only option was to file a new FOIA for the missing pages. After being denied a waiver for the fees, he sought out crowdfunding help.

He’s not the only one. A quick search on GoFundMe brought up dozens of campaigns for FOIA crowdsourcing related to requests made to all levels of government. Greenewald said this is only his second time resorting to crowdfunding for the Black Vault, out of the 9,000 he estimated he’s sent over his lifetime. “And that doesn’t count the follow-ups,” he said.

“It’s the best feeling in the world to go to your mailbox and see in there a declassified document that no one in the general public has ever seen before,” said Greenewald, when I asked him what motivates him to keep FOIA-ing. In some cases, the battle can last over a decade—his record is 14-and-a-half years of arguing for a World War II-era document on weapons to be released. Even if the documents don’t reveal a massive cover-up or other government misdeeds, he said, what’s important is our ability to access them.

“We shouldn’t be afraid to ask questions,” he said.