A former Florida tax collector whose arrest led to a federal investigation into the US congressman Matt Gaetz has been sentenced to 11 years in prison for sex trafficking of a minor and other offenses.

Joel Greenberg, former tax collector for Seminole county, was accused of stalking a political opponent, public corruption, making fake licenses and scheming to submit false claims for a federal loan.

He pleaded guilty to six federal crimes, including identity theft, stalking, wire fraud and conspiracy to bribe a public official. Prosecutors said he paid at least one girl to have sex with him and other men.

“Nothing justifies my actions. My conduct is so shameful. I feel remorse for what I’ve done,” Greenberg said on Thursday before US district judge Gregory Presnell sentenced him in an Orlando courtroom.

Greenberg also directly apologized to the residents of Seminole county, his family and a schoolteacher he smeared when the educator decided to run against him.

Presnell said that in his 22 years as a federal judge, he had never experienced a case like Greenberg’s and “a defendant who has committed so many different types of crimes in such a short period of time”.

Greenberg’s attorney had asked for leniency, saying that his client had assisted in investigations of 24 people, including eight for sex crimes. Defense attorney Fritz Scheller said that Greenberg’s cooperation had led to four federal indictments, and that he believed additional ones were expected in the coming month.

Greenberg’s cooperation could play a role in an investigation into his friend Gaetz over whether he paid a 17-year-old girl for sex. Gaetz has denied the allegations and previously said they were part of an extortion plot. No charges have been brought against the Republican congressman, who represents a large part of the Florida Panhandle.

Greenberg has been linked to other Florida politicians and their associates. So far, none has been implicated in the sex trafficking investigation.

After the hearing, Scheller called Greenberg’s sentence just.

Scheller said he was shocked that Greenberg’s cooperation had not yet resulted in more prosecutions and that Greenberg had been in communication with federal investigators in the past three months. When asked whether he thought others would be charged with sex crimes, the defense attorney said, “I do.”

“There should be, and I think part of my frustration is that I have a pretty good insight into the evidence in this case,” Scheller said.