DALLAS -- Among the peaceful marchers in Dallas Thursday, officials say 20-to-30 carried rifles.

The armed protesters were also peaceful, but police had to make quick assessments when they started taking rifle fire from multiple locations.

In the wake of the attack, Dallas Mayor Mikes Rawlings said Dallas police had detained 20 people who were wearing camouflage and fleeing the gunshots last Thursday before releasing them all. One of those detained was Mark Hughes, who police wrongly identified as a suspect. Hughes was carrying a rifle in the protests before the shooting began, and video showed him handing his weapon to an officer in the chaotic aftermath.

A Facebook Live video showed Mark Hughes handing his weapon to police.
A Facebook Live video showed Mark Hughes handing his weapon to police.

It's not the first time someone has been detained or arrested after bringing a rifle to a protest.

In June, two men carrying rifles accompanied marchers in Arlington protesting the police shooting of a Black teen.

Texans can openly carry long guns. But according to Texas law, it is not legal to "display a firearm or other deadly weapon in a public place in a manner calculated to alarm."

Arlington police arrested an armed demonstrator on that charge.

"It's very, very clear if you brandish the gun and point it at me, you're doing it in a manner to alarm. But frankly, that doesn't happen very often,” Sanford Levinson said. “Do you really have to wait until someone is pointing a gun at you in order to feel nervous?”

Levinson is a Second Amendment scholar and UT law professor. He sees a bigger problem with open carry laws.

Sanford Levinson spoke to us via Skype.
Sanford Levinson spoke to us via Skype.

"The police are doing a very tough job,” he said Monday. “We've made it harder for them to do their job by increasing the likelihood that they're going to run into armed citizens."

Professor Levinson says the Second Amendment does not prevent state or local lawmakers from restricting where and when we can carry guns. But he expects another Second Amendment battle soon on that question.

"We'll know the answer to your question after the next election, and after new judges have been appointed,” he said.

Armed open carry protesters in Austin.
Armed open carry protesters in Austin.