Enrique Tarrio, the chairman of the Proud Boys, a far-right nationalist group that is a major target of the sprawling investigation into the riot at the Capitol this month, has a history of cooperating with law enforcement, according to court records and a former prosecutor.
The stunning revelation that Mr. Tarrio, who leads one of the country’s most notorious extremist groups, helped the F.B.I. and local police departments go after more than a dozen criminal defendants about a decade ago was first reported by Reuters on Wednesday.
The news emerged as Mr. Tarrio himself has fallen under scrutiny for his role in encouraging the Proud Boys to attend a “Stop the Steal” rally in Washington on Jan. 6, after which a mob of hundreds broke into the Capitol, disrupting the final certification of the presidential election.
“Mr. Tarrio was a cooperator — like many who seek to provide information and try to obtain substantial assistance,” the former prosecutor, Vanessa S. Johannes, wrote in an email.
The court transcript, which documents a hearing in 2014 where Mr. Tarrio sought to reduce his own sentence in a fraud case, shows that he helped law enforcement officers in his home state, Florida, to investigate and prosecute criminal enterprises, including an illegal gambling business, a marijuana grow lab, an operation that sold anabolic steroids and an immigrant smuggling ring.
Mr. Tarrio did not respond to messages from The New York Times seeking comment, but he denied to Reuters that he had ever worked undercover or cooperated with law enforcement.
“I don’t know any of this,” he said. “I don’t recall any of this.”
Mr. Tarrio, 36, has been a focus of the F.B.I.’s enormous inquiry into the Capitol attack, which has led so far to more than 150 arrests, including those of at least six members of the Proud Boys. The group of self-described “Western chauvinists” has a history of scuffling in street fights with left-wing antifascist activists and has made a name for itself in recent years for its vocal — and often violent — support of former President Donald J. Trump.
Although Mr. Tarrio went to Washington earlier this month, he was arrested by the local police on suspicion of burning a Black Lives Matter banner torn from one of the city’s Black churches during a separate round of protests in December.
After he was thrown out of the city by a judge, he posted messages online encouraging the Proud Boys to attend the rally on Jan. 6, not in their typical black-and-yellow polo shirts, but instead “incognito.” Federal agents cited the messages in their criminal complaint against one of Mr. Tarrio’s top lieutenants, Joseph Biggs, who was arrested last week.
Mr. Tarrio’s criminal history reaches back to at least 2004 when he was convicted of stealing a $50,000 motorcycle. In 2012, he was charged with fraud in Miami in connection with a scheme to sell loads of diabetes test kits that co-defendants had stolen from a truck in Kentucky and was sentenced to 30 months in prison. “He was kind of like the marketing person,” his lawyer, Jeffrey Feiler, said at the time.
In July 2014, Mr. Feiler went to court to ask a federal judge to reduce Mr. Tarrio’s sentence, arguing that his client had cooperated “in a significant way” in two other federal cases, leading to the prosecution of 13 people. Mr. Feiler also noted that Mr. Tarrio had worked undercover for police departments in Miami and Hialeah, at times putting himself at risk.
“I find that the defendant has provided substantial assistance in the investigation and prosecution of other persons involved in criminal conduct,” the judge in Mr. Tarrio’s case, Joan A. Lenard, ruled.
She ultimately cut his sentence to 16 months.
While there is no evidence that Mr. Tarrio has continued to help the authorities fight crime, Mr. Feiler believed at the time that his client was good at it.
“Frankly, in all the years, which is now more than 30 that I’ve been doing this,” he said at the hearing, “I’ve never had a client as prolific in terms of cooperating in any respect.”