(CNN) -- Just 12 miles south of the spot where a police officer killed Michael Brown, it happened again: Another 18-year-old died at the hands of police Wednesday.

An off-duty officer opened fire on the teen, and the policeman didn't stop until he'd fired his weapon 17 times, authorities say.

Anger erupted among residents, who damaged police cars, and they pointed to what they felt were parallels to the Brown shooting. But in reality, the similarities are slim.

Yes, the teen was black. And the officer was white. Yes, the officer fired several times. And it all unfolded in the St. Louis metro area.

But the commonalities end there.

In this case, the 18-year-old was armed, and he fired on the officer first, St. Louis Police Chief Sam Dotson said.

The death comes on the heels of the Brown shooting two months ago in the suburb of Ferguson, and just ahead of a "Weekend of Resistance" in St. Louis, where activists will push for movement in the investigation into that case.

Tensions are already high in the community, and it's uncertain how the latest shooting will affect its mood.

"At the scene of yet another young man's death," tweeted St. Louis Alderman Antonio French. "This happens too often in our city. It's a crisis that we should all be concerned about."

An animated crowd quickly gathered late Wednesday near the site close to the Missouri Botanical Garden, chanting slogans as St. Louis police officers stood by.

"Hey, hey, ho, ho, these killer cops have got to go," the crowd chanted, repurposing a popular chant from the Brown protests.

The confrontations with police were intense and laced with profanity.

"That was somebody's baby," screamed one man, referring to the man who was killed.

"Think about your own child," pleaded another person in the crowd.

Despite the tensions, Dotson said no businesses were looted and no windows were smashed. He praised officers for showing a "tremendous amount of restraint" as members of the crowd confronted them face-to-face and damaged police cruisers.

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The officer, a six-year veteran of the force, was working a second job for a security company, one that was approved by his department. He was wearing his police uniform.

While on patrol, the officer saw three black males run away as he approached. He gave chase because one of them was holding up his pants in a way that made the officer believe the teen may be carrying a gun, Dotson said.

The officer and one of the three tussled. The teen ran off, then turned around and fired at least three shots at the officer, Dotson said.

The officer returned fire, killing the teen.

Police recovered a 9 mm handgun. And Dotson said the teen was "no stranger to law enforcement." He didn't offer details, citing privacy concerns.

The two other males have not been apprehended.

In August, the death of the unarmed Brown fueled protests and sparked a nationwide debate on police use of force.

Protesters are planning a series of demonstrations, rallies and events in Ferguson and St. Louis this weekend to call for an end to racial profiling and what they call police violence.

This weekend's protests start with a rally outside the office of the prosecutor investigating the Brown shooting.

Demonstrators will call for Bob McCulloch to step aside and allow a special prosecutor to be appointed.

Additional marches and demonstrations will mark the weekend, along with "civil disobedience actions around the St. Louis region," according to a statement from organizers that also says thousands of people from across the country are expected.

CNN's Dave Alsup, Tony Marco and Dana Ford contributed to this report.