The individuals were detained in a controversial mass arrest that took place on two downtown bridges.
St. Paul City Attorney John Choi says he thinks police acted appropriately in arresting the crowds.
But he says prosecutors have a different threshold when deciding whether to bring a case to trial.
"There was a lot of confusion for a lot of people that night. Ultimately, our decision reflects our prosecution standard, which is, 'Can we prove the charges beyond a reasonable doubt at trial?'" Choi explained. "We've come to the conclusion that for the cases involving the Marion Street Bridge and the Cedar Street Bridge, that would not be the case."
That means all the charges against 323 people will be dropped.
Peace activist Daniel Wilhelmsen, 19, of Minneapolis was one of the people arrested. He says the police action that night was totally unjustified.
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"It was a rally for peace that they ended with violence," he said.
Wilhelmsen acknowledges at one point, he could have left the scene without arrest. But by the time he and his friends decided to take off, it became clear to him that the police were going to round up everyone.
"We were all holding up peace signs, and we're asking, 'How can we leave? How can we peacefully exit?'" Wilhelmsen said. "A bike cop told us, 'Exit to the bridge.' We looked at the bridge and saw the blockade. And we're like, 'No, no no, we want to leave.'"
But that's when an officer sprayed him and a friend with pepper spray.
Wilhelmsen said he's looking forward to clearing his record of the unlawful assembly charges. But he says a backpack confiscated from him that night has still not been returned.
City Attorney John Choi says authorities are continuing to investigate 20 remaining cases stemming from the bridge arrests.
They are suspected of offenses ranging from providing false information to police to running away from officers.
In all, the St. Paul attorney's office has dismissed about three-fourths of the 672 arrest cases that took place during the convention. A handful of more serious felony cases are pending.