What's the difference between being told to "disperse" and being ordered to "leave?" One might get you convicted of trespassing at the Mall of America. The other will not.

That explains why Bloomington prosecutors have dropped trespassing charges against the organizers of a Black Lives Matter protest at the Mall of America in December. While mall officials that day told the group repeatedly over a loudspeaker that the demonstration was unauthorized, they forgot to use one key word: leave.

"For a good trespass case, somebody in a position of authority must tell you you have to leave the property," Bloomington City Attorney Sandra Johnson said Wednesday.

The mall's announcement simply told the crowd to "disperse," said University of St. Thomas Law School Professor Nekima Levy-Pounds, who helped organize the protest.

"Disperse means to spread or to spread out," she said, "and that's what we did."

Levy-Pounds and other organizers face other charges related to the protest, including unlawful assembly. Trespassing charges still stand against protesters arrested by police that day, because the cops used the right words.