As the debate over President Donald Trump’s voter fraud commission intensifies, a new study has found 8,471 instances of double voting during the 2016 elections occurring in 21 states.

The nonpartisan Government Accountability Institute (GAI), which was cofounded by Breitbart News Senior Editor-at-Large Peter Schweizer and former Breitbart Executive Chairman Stephen K. Bannon, analyzed data from 21 U.S. states and found that 7,271 ballots were cast in more than one state by individuals with the identical first and last name, middle initial, birthdate, and partial Social Security number. Another 1,200 double votes meeting the same criteria were detected within the same state. Given the high methodological bar employed, GAI says the statistical “probability of correctly matching two records with the same name, birthdate, and Social Security number is close to 100 percent.”

The 37-page study is unique in that while most past voter fraud analyses have used statistical models to project fraud rates, the GAI report identified actual matches of real votes cast using public voter information rolls. “There are currently no government agencies or private entities that compare all state voter rolls to detect duplicate voting fraud,” states the report.

GAI says the reason it only examined 21 states is because the government watchdog group encountered numerous hurdles in gathering state voter data, including: “exorbitant costs,” woefully disorganized and incomplete data, and “outright rejected requests” from states. Still, “extending GAI’s conservative matching method to include all 50 states would indicate an expected minimum of 45,000 high-confidence duplicate voting matches,” says the report.

The same individual casting more than one ballot represents an aggressive form of voter fraud; other types of voter fraud can include falsifying registration information, destroying ballots, or noncitizen voting. GAI says the 8,471 instances of double voting it uncovered “should be investigated to determine whether two votes were cast by the same person or if identity theft occurred.”