St. Louis had a law-and-order crisis long before these protests

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(CNN)Jason Stockley, the white ex-police officer whose Friday acquittal in the death of Anthony Lamar Smith has sparked days of protests, may not have even faced trial without the "Ferguson Effect."

Stockley, a former St. Louis police officer, shot and killed Smith, a 24-year-old suspected drug dealer, nearly three years before a Ferguson police officer shot and killed Michael Brown. But he wasn't charged until May 2016 — almost two years after Brown's August 2014 death, which sparked riots that gained national attention.
"Without the Mike Brown case ... the prosecution of Jason Stockley never would have happened," CNN's Thomas Lake wrote last month in a report on the so-called "Ferguson Effect."
People overturn trash cans and throw objects as police try to clear a violent crowd on Sept. 16, 2017, after Stockley's acquittal.
The concept suggests that police have faced increased scrutiny after Brown's death — so much so that some officers may be more hesitant to use force, even when necessary, because they fear backlash.
    After the 2014 shooting, the Ferguson police department lost a third of its officers, and "those who remained were more cautious than before," Lake wrote.
    For example, traffic stops fell by nearly 75%.
    But at the same time, crime ticked up: Violent crime rose by 65% in Ferguson, a suburb of St. Louis, in the first year after Brown's death. Also, homicides went from two in 2014, to nine in 2016.
    No one can say for sure why crime increased after Brown was shot to death, but Ferguson Mayor James Knowles III has a theory — and it all starts with traffic stops.
    Ferguson affected us all, police say
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      Ferguson affected us all, police say


    Ferguson affected us all, police say 03:02
    "Knowles spent five years as a Ferguson police dispatcher, getting a sense of what officers do and why they do it, and he gained an appreciation for the role of the traffic stop. It was not just about revenue, he said. It was about vigilance," Lake wrote. "If a car had the wrong plate, it might be stolen. If the car was stolen, the driver might be wanted for other crimes. If the driver was wanted for other crimes, he might be carrying an illegal gun, and he might be on his way to yet another crime."
    The mayor said he frequently hears motorcycles drag racing in the middle of the night near his home, and no police officers stop the drivers.
    "Whoever's doing it feels like they can do whatever the hell they want," Mayor Knowles said. "And if you feel like you can do whatever the hell you want, you're going to do all kinds of stuff."

    Why Jason Stockley was on trial

    Protesters in St. Louis, after Stockley's acquittal.
    Though no one can definitively prove if the Ferguson Effect is real, civil rights activists and police union officials say Stockley's prosecution wouldn't have happened without the Brown case.
    Stockley shot and killed Smith in 2011 after a police chase. The former officer said he fired because he believed Smith was reaching for a weapon. Stockley eventually left the department, and the city settled a wrongful-death suit with Smith's family for $900,000, but state and federal authorities declined to seek criminal charges.
    That changed in 2016, when then-St. Louis Circuit Attorney Jennifer Joyce charged Stockley with first-degree murder, citing new evidence.
    Prosecutors argued Stockley planted the gun recovered inside of Smith's car — but a judge ultimately ruled that the weapon was too large for Stockley to hide from cameras at the scene.
    More than 120 people have been arrested during protests since Stockley's Friday acquittal.
    This story has been updated to reflect the latest number of people arrested since Friday.
    CLARIFICATION: A previous version of this story reported that the St. Louis Metropolitan Police Department fired Jason Stockley in 2013. The police union says he resigned and Stockley's attorney says he retired. The police department would not confirm the circumstances of his departure.