The Mexican national accused of breaking into North Korea's Spanish Embassy

Adrian Hong Chang and nine others are accused of breaking into Pyongyang's diplomatic compound in the Spanish capital before the group began to "violently strike its occupants" and detain and handcuff them, Spain's judicial authorities said in a news release. They also tried and failed to get one man to defect, authorities said in the statement.

The name Adrian Hong is well known in North Korean human rights activist circles. A person by that same name testified before the Canadian Senate in 2016 criticizing the Kim regime. CNN's attempts to reach Hong for comment were unsuccessful.

Spanish authorities had kept the case under wraps until Tuesday, when Judge José de la Mata ordered court documents unsealed. According to those court documents, Hong -- a Mexican national and US resident -- was the one who led the assault.

Spanish authorities said that Hong fled Spain after the attack for Lisbon, before making his way to the United States. He then got in touch with the FBI to share information "relevant to the incident as well as audiovisual material supposedly obtained," per Spanish judicial authorities.

The FBI declined to comment on the case.

Hours after Judge Mata's statement was released, a Korean activist group dedicated to overthrowing the Kim regime called the Cheollima Civil Defense (CCD) released a statement claiming responsibility for the incident.

The group said it was responding to an "urgent situation" and was "invited into the embassy." CCD denied it had used any violence.

The Cheollima Civil Defense first gained international recognition after it reportedly provided refuge for Kim Han Sol, the son of Kim Jong Nam. Kim Jong Nam, the elder half-brother of North Korea's leader, was exposed to the deadly nerve agent VX in 2017 while entering an airport in Kuala Lumpur, killing him in minutes. US, South Korean and Malaysian authorities have pinned the attack on Pyongyang, but North Korea has adamantly denied any responsibility.

Lawyer Lee Wolosky, who represents the group, said there "there are a number of statements attributed to the Judge in media reports that do not accurately reflect what happened in Madrid."

"It was, in any event, highly irresponsible to disclose publicly the names of people who are working in opposition to a brutal regime that routinely and summarily executes its enemies," Wolosky said in a statement to CNN.

"The Spanish judge purported to reach conclusions without any input from representatives of Free Joseon," Wolosky said, using another name that CCD goes by.

The Cheollima Civil Defense said in its statement that revealing the identity of its members could put them in danger. The group accused US government sources of leaking their role in the raid to the media, and thereby committing "abhorrent acts pursued in the name of political expediency, in service to a regime who has tortured and killed millions."

"Some of us will be imprisoned, tortured or killed in the course of this fight. But to share information that may help identify any of us who take risks to protect others is to aid and abet the regime in Pyongyang," the statement read.

Hong is a known commodity among the close-knit group of activists, journalists and academics who cover human rights in North Korea.

As a college student, Hong helped found Liberty in North Korea, an NGO that has helped hundreds of North Koreans defect.

However, Hong has "had no involvement with the organization for over ten years," Hannah Song, the organization's current CEO, said in a statement.

"We have no knowledge of his recent activities, and we have no information on the Madrid Embassy incident other than what has been published by the media."

In recent public appearances, Hong has been identified as president of the Joseon Institute, a think tank studying "increasingly imminent, dramatic change" in North Korea.

Jean Lee, a North Korea expert at the Wilson Center, said she remembers Hong from speaking on a panel with him in 2012.

"He's a very intense guy and very committed to North Korea and very dogmatic," Lee said. "He comes up in conversation on a regular basis in that circle."

Lee, who as a reporter for The Associated Press opened the company's bureau in Pyongyang, told CNN she had no knowledge of Hong's involvement with the group before media reports first surfaced, but said she long suspected that the person behind the mysterious group was not a native Korean speaker. Lee said that English versions of their announcements were grammatically sound but they usually seemed stilted in Korean, as if they were translated verbatim.

The group also used a distinctly South Korean spelling of Cheollima, Lee said.