NEW YORK - A Florida white supremacist organization told the Anti-Defamation League on Thursday that the 19-year-old gunman who stormed into his former high school and murdered 17 people was a member of their group. A spokesperson for the Republic of Florida (ROF), which describes itself as an “white civil rights” group with an “organized militia,” confirmed that Nikolas Cruz was associated with their movement.Jordan Jereb, the leader of the white supremacist group, said that Cruz had joined the group, but later said that he did not know whether that was true, according to The New York Times.Cruz reportedly admitted to the massacre on Thursday after he was brought before a judge via video conference at the Broward County court, according to The Washington Post. The teenage killer was charged with 17 counts of premeditated murder after entering into Marjory Stoneman Douglas High School with a semiautomatic rifle on Wednesday and began firing randomly at students and teachers on campus.The ADL said that they contacted Jareb after self-described ROF members claimed on the discussion forum 4chan that Cruz had been apart of the neo-Nazi organization. He later walked back the claim, saying that he could not confirm the information. ROF reportedly has members in north and south Florida and borrows paramilitary concepts from a disparate anti-government extremist militia movement.The Florida-based supremacist group reportedly has contact with several other white nationalist organizations, including the Vinlanders Social Club, the League of the South, and Atomwaffen. Following the shooting, The ADL pleaded with lawmakers to make it a top priority to end the “epidemic of gun violence” in America, and called the climate of fear hovering over school campuses “outrageous.”“We demand that our elected leaders come up with strategies to deal with this epidemic of gun violence plaguing our country,” Jonathan Greenblatt, CEO of the ADL, said in the statement. “It is outrageous in a country such as ours that teachers and kids can’t go to school without fear of being shot.”Jareb was arrested on charges of threatening a staffer in the office of Florida Governor Rick Scott in 2016 because he was allegedly angry at the staffer’s son. In 2014, before he founded ROF, Jereb said on social media that “the traitors of my country (Florida) will be hung in our courts,” according to the ADL. The school shooting at Marjory Stoneman Douglas is the third deadliest school shooting in US history and marks the 18th gun-related shooting incident on campus in 2018.