The Police officer, Jeronimo Yanez, who is Latino, was acquitted on Friday of manslaughter and two other charges.
The incident, one of several deaths of black men and boys shot by USA police, sparked outrage and protests in St Paul. It was inevitable that protests and rallies would arise, as they did in St. Paul Friday night.
About 200 people turned out for that demonstration in Minneapolis - the state's largest city that borders St. Paul - according to the Star Tribune newspaper.
A protester raises her hands after being contained by law enforcement, while being arrested during a march on Interstate 94 after a jury found St. Anthony Police Department officer Jeronimo Yanez not guilty of second-degree manslaughter in the death of Philando Castile, at the Minnesota State Capitol in St. Paul, Minnesota, U.S., June 16, 2017.
When some marchers ignored repeated police orders to disperse, state and local officers arrested 18 of them shortly after midnight, a state police spokesman said. In light of the officer's clearance, black gun owners are concerned about admitting they are licensed to carry to police officers, reports NBC Washington.
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She says those arrested were booked at Ramsey County Jail on charges including being a pedestrian on the busy freeway.
Yanez shot into Philando Castile's vehicle seven times after Castile told him he was carrying a gun.
Rick Ector, a licensed gun owner who resides in Detroit said, some Police officers can be stereotyped when dealing with black riffle owners. And Yanez said he feared for his life.
U.S. Senator Al Franken of Minnesota on Saturday said Castile did not deserve to die.
"Philando was murdered in cold blood and will not be here this Father's Day for Dae-Anna", a Facebook event page said.