Flashing supporters a broad smile and a peace sign, demonstrator Anna Marie Stenberg was released Wednesday after nearly 20 hours in federal custody for scaling the 8-foot security fence outside the Democratic National Convention.

The 69-year-old activist, no stranger to protest arrests, was one of four Bernie Sanders supporters charged Tuesday with a federal crime for entering the restricted zone surrounding the Wells Fargo Center.

But lawyers for Stenberg and the others called their arrests arbitrary and questioned Wednesday why they face possible criminal records while other demonstrators walked away with only $50 civil citations. Each vowed to fight the charges in court.

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"I'm very concerned about the expansive use of federal power to designate certain locations to be national security sites to the exclusion of First Amendment rights," said Stenberg's Center City lawyer, Paul Hetznecker. "I think it's a dangerous precedent for our democracy and our civil rights."

Stenberg and the others - Katherine Roberts, 37, of Georgia; Barbara Burns, whose age was unavailable, of Boston; and James Williams, 19, of Towson, Md. - were released Tuesday on their own recognizance. Each could face up to a year in prison if convicted.

According to the U.S. Secret Service, the four scaled the fence during protests Tuesday evening. The day's demonstrations included more than 5,000 participants in eight protests.

But despite the volume, Philadelphia police seemed hesitant to place all but the most unruly demonstrators under arrest, opting instead to briefly detain problem protesters at the scene, issuing $50 civil citations and then releasing them.

Officers had issued nearly 70 citations as of Wednesday afternoon, and at times have appeared downright accommodating to demonstrators.

One video posted to Twitter on Monday showed an orderly line of protesters queuing up to jump over a 3-foot barricade as officers, zip-ties at the ready, waved them over, one by one.

What set apart Stenberg and the others who were charged, federal authorities said, was that they scaled the taller fence erected by federal authorities to designate the area a national security perimeter.

Susan Lin, a Center City lawyer for Georgia protester Roberts, said her client had no way of knowing that difference in penalties between the two barriers.

"I think it's unfortunate for some protesters that they just happened to be caught in that Secret Service perimeter versus a city perimeter," Lin said. "All she knew was that she was engaging in an act of civil disobedience."

Speaking to reporters Wednesday, Police Commissioner Richard Ross acknowledged the possibility for confusion and said federal authorities already had indicated they might be willing to drop the federal charges against Stenberg and the others, leaving them city-issued citations.

"The reason we were concerned about it is because we don't believe those people knew" that climbing the fence would result in federal charges, Ross said.

But that approach - if it is used - would apply only to Tuesday's cases, Ross said.

"That is a restricted area, so people should know from this point forward: If you breach that fence, it is not Philly PD and the District Attorney or anyone else that you'll be dealing with," he said. "You'll be dealing with the United States government."

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Staff writer Chris Palmer contributed to this article.

[Updated: This article has been updated to correct the spelling of Anna Marie Stenberg.]