MIAMI -

An associate of former U.S. Rep. David Rivera has agreed to a plea deal involving alleged illegal contributions to a previously unknown candidate.

Ana Alliegro accepted the plea deal Tuesday in Miami federal court. She originally pleaded not guilty to all four campaign finance violations.

Also Monday, Rivera was named as a co-conspirator for the first time.

"Why do we keep not naming the co-conspirator," the judge asked during the hearing.

"That's Justice Department policy, your honor, not to name an unindicted co-conspirator," the prosecutor answered.

The plea might mean Alliegro could be helping prosecutors build their case against Rivera.

However, her attorney said there was no guaranteed benefit by pleading guilty.

"She's just accepted responsibility for what she's done," attorney Richard Klugh told Local 10 News.

An indictment charged that Alliegro illegally funneled more than $80,000 to the 2012 primary campaign of Democrat Justin Lamar Sternad, a political novice who pleaded guilty last year to federal campaign violations.

The investigation centers on allegations that Rivera, a Republican, was using Sternad to weaken his Democratic rival and eventual winner, U.S. Rep. Joe Garcia.

Alliegro was arrested in March after she fled to Nicaragua.

Sternad, who pleaded guilty and was sentenced to seven months in prison, told Local 10 he felt used by Alliegro and Rivera. Sternad claimed he thought his campaign was legitimate until he inadvertently saw some of Alliegro's paperwork.

"It was a receipt for congressman Rivera's qualifying fee, so I was like, 'Hey, what's this?'" Sternad said. "She made light of it, said it was just something that was, you know, business as usual."

Should it become necessary, Sternad said he would "absolutely" testify against Rivera. His surrender date is Sept. 25.

Rivera, who is running for his former congressional seat, has denied any wrongdoing.

Follow Glenna Milberg on Twitter @GlennaOn10

Follow Peter Burke on Twitter @PeteBurke

Follow Local 10 on Twitter @WPLGLocal10