(CNN) The protests happen with such frequency, the images seem like deja vu: Demonstrators flooding city streets, demanding an end to excessive police force and chanting "black lives matter."
But each case that spurs "black lives matter" marches has different circumstances -- and different outcomes. Here are how some high-profile cases have turned out:
Trayvon Martin, 17
George Zimmerman, left, and Trayvon Martin
Date of death: February 26, 2012
Where: Sanford, Florida
What happened: Martin was walking from a convenience store back to the home of his father's fiancee. Neighborhood watch volunteer George Zimmerman spots him from his car and calls 911, reporting "a real suspicious guy."
"This guy looks like he's up to no good, or he's on drugs or something," Zimmerman told a dispatcher. "It's raining, and he's just walking around."
A scuffle broke out, but there were no direct witnesses. Zimmerman claimed Martin attacked him, hitting him in the nose and knocking him onto the pavement. Zimmerman said he then took out his gun and shot Martin in self defense.
But critics said Zimmerman was unjustified in confronting the unarmed teen, especially since Zimmerman didn't heed a police dispatcher's advice to stop following him.
The outcomes: Zimmerman was charged with second-degree murder but was found not guilty. The acquittal ignited protests across the country, and the "Black Lives Matter" movement gained national prominence.
The case also led to the firing of Sanford Police Chief Bill Lee, who was criticized for not arresting Zimmerman after Martin was killed.
Why this verdict? Five things that led to Zimmerman's acquittal
Eric Garner, 43
An NYPD officer puts Eric Garner in a prohibited chokehold.
Date of death: July 17, 2014
Where: New York City
What happened: Police tried to arrest Garner in front of a store for allegedly selling cigarettes illegally. Garner raised both hands and told officers not to touch him. Seconds later, Officer Daniel Pantaleo grabbed the 350-pound man in a chokehold and pulled him to the sidewalk, rolling him onto his stomach.
The New York Police Department prohibits the use of chokeholds.
Garner, who had asthma, repeatedly said, "I can't breathe! I can't breathe!" while several officers restrained him on the ground. Police said he suffered a heart attack and died en route to a hospital.
The outcomes: A grand jury declined to indict Pantaleo, sparking protests and "die-ins."
Photos: Athletes wearing 'I can't breathe' shirts
Members of the Georgetown basketball team wear "I can't breathe" shirts as they stand for the national anthem before a home game Wednesday, December 10, in Washington. The shirt references the words spoken by Eric Garner, a 43-year-old man who died earlier this year after being put in a chokehold by a New York City police officer. After a grand jury decided not to bring criminal charges against the officer, demonstrators across the country
took to the streets to express their outrage.
Portland Trail Blazers Wesley Matthews, left, and Dorell Wright wear the shirts while warming up for a game in Minneapolis on December 10.
Kobe Bryant and the Los Angeles Lakers wear the shirts before a home game Tuesday, December 9.
Wearing the shirts from left are Lakers Nick Young, Jordan Clarkson, Carlos Boozer, Wayne Ellington and Jeremy Lin.
LeBron James of the Cleveland Cavaliers wears the shirt in New York before playing the Brooklyn Nets on Monday, December 8.
San Diego Chargers linebacker Melvin Ingram shows his solidarity with Garner before playing New England on Sunday, December 7.
Detroit Lions running back Reggie Bush warms up before a home game on December 7.
Cleveland Browns cornerback Johnson Bademosi shows his support for Garner before playing a game in Cleveland on December 7.
Chicago Bulls star Derrick Rose was the first major athlete to wear the shirt, making headlines Saturday, December 6, in Chicago. "I could care less about who else weighs in on this," he said. "Usually athletes tend to stay away from this, but I just felt as if I had to do something."
Garner's death also spurred a new protest slogan: "I can't breathe," referring to some of his final words before he died. Several professional athletes wore shirts saying "I can't breathe" in silent protest.
Pantaleo offered his condolences to Garner's family and said he never intended to hurt Garner. The police union defended Pantaleo, saying he just wanted to take Garner into custody after the suspect resisted.
New York City eventually settled with Garner's family for $5.9 million. City Comptroller Scott Stringer said the settlement "acknowledges the tragic nature of Mr. Garner's death," but "the city has not admitted liability."
Michael Brown, 18
Officer Darren Wilson, left, and Michael Brown
Date of death: August 9, 2014
Where: Ferguson, Missouri
What happened: Brown was walking with a friend in the middle of a street when Ferguson Police Officer Darren Wilson approached them and told them to walk on the sidewalk.
After that, the narratives varied enormously. Authorities said Brown had attacked the officer in his car and tried to take his gun. Others said the teenager was surrendering, his hands in the air to show he was unarmed, when the officer opened fire. Documents showed that Wilson fired his gun 12 times.
What happened when Michael Brown met Officer Darren Wilson
The outcomes: A grand jury decided not to indict Wilson -- leading to heated and sometimes violent protests in Ferguson and across the country.
Unrest in Ferguson
Police officers walk past the smoldering remains of a beauty supply store in Ferguson, Missouri, on Tuesday, November 25. Ferguson has been struggling to return to normal since Michael Brown, an unarmed black teenager, was killed by Darren Wilson, a white police officer, on August 9. The grand jury did not indict Wilson in the case, prompting new waves of protests in Ferguson and
across the country.
A woman cleans up glass from a business' shattered window on November 25.
A Ferguson firefighter surveys rubble at a strip mall that was set on fire overnight.
Protesters run away after police deployed tear gas in Ferguson on Monday, November 24.
Police take position during clashes with protesters on November 24.
A protester stands in front of police vehicles with his hands up on November 24.
Police in riot gear move past a burning vehicle on November 24.
A looter in Ferguson walks out of a burning Walgreens on November 24.
Riot police clash with protesters on November 24.
Firefighters work on extinguishing a Little Caesars restaurant on November 24.
Smoke fills the streets of Ferguson as buildings burn on November 24.
Police officers grab a protester on November 24.
A woman treats her face for possible tear gas exposure on November 24.
People walk away from a burning storage facility on November 24.
A man steps out of a vandalized store on November 24.
A police officer runs by a burning police car on November 24.
Police officers stand guard as protesters confront them on November 24.
Protesters block streets in St. Louis after the announcement of the grand jury's decision on November 24. Ferguson is a suburb of St. Louis.
Police confront protesters in Ferguson on November 24.
A police officer points his rifle at demonstrators on November 24.
Protesters run for shelter as smoke fills the streets of Ferguson on November 24.
The glass windows of a store are shattered on November 24.
A demonstrator listens to a car radio as the grand jury's decision is delivered in front of the Ferguson Police Department.
Lesley McSpadden, mother of Michael Brown, is escorted away from the Ferguson Police Department on November 24.
A group of protesters vandalizes a police vehicle in Ferguson on November 24.
Police officers confront protesters on November 24.
Demonstrators block traffic during a protest in front of the Ferguson Police Department on November 24.
Demonstrators gather outside the police station on November 24.
Protesters gather as they wait for the announcement of the grand jury decision on November 24.
Members of the media line up in a parking lot across from the Buzz Westfall Justice Center on November 24.
Residents begin to gather at the Michael Brown memorial ahead of the grand jury announcement.
National Guard troops arrive ahead of the grand jury announcement.
Members of the Missouri National Guard are escorted out of the Buzz Westfall Justice Center.
Demonstrators are confronted by police as they block a street before the grand jury announcement.
A few days later, Officer Wilson resigned from the Ferguson Police Department.
Despite the lack of criminal charges, the Michael Brown case launched a series of reforms. A federal investigation revealed a pattern of abuse by Ferguson's mostly white police force against the city's majority black residents.
The Justice Department found that "many officers" apparently viewed some of the city's black residents "less as constituents to be protected than as potential offenders and sources of revenue."
Black residents were ticketed and cited for minor violations at a higher rate than white residents, the Justice Department said. The investigation also found a spate of racist emails sent by some police and court officials.
Ferguson police report: The most shocking parts
After the scathing Justice Department report, Ferguson police Chief Thomas Jackson resigned.
And in February, the Justice Department sued Ferguson to force police reform in the city.
Walter Scott, 50
Date of death: April 4, 2015
Where: North Charleston, South Carolina
What happened: Officer Michael Slager pulled Scott over for a broken taillight. Scott bolted out of his car, though it's not clear why. His family attorney speculated that Scott's flight stemmed from his unpaid child support "and a fear of maybe going back (to jail)."
As Scott ran away from the officer, a witness captured video of Slager shooting Scott several times in the back.
Who was Walter Scott?
The outcomes: The North Charleston Police Department fired Slager, and a grand jury indicted him on a state murder charge.
A federal grand jury also indicted Slager for misleading investigators and violating Scott's civil rights.
After Scott's death, the South Carolina Legislature passed a bill mandating the use of police body cameras.
And the North Charleston City Council agreed to a $6.5 million settlement with Scott's family.
Freddie Gray, 25
Date of death: April 19, 2015, seven days after he was fatally injured
Where: Baltimore
What happened: An officer on bike patrol made eye contact with Gray, and Gray fled. Police later found a knife in Gray's pocket and arrested him on a weapons charge.
Officers put Gray in a police van. At some point, Gray somehow suffered a fatal spinal cord injury. He died seven days later.
Gray's death prompted riots, looting and arson in Baltimore.
The outcomes: Six Baltimore police officers, including three black and three white officers, were charged in connection with Gray's death.
Baltimore officers in Freddie Gray case
Six Baltimore police officers were charged in the April 2015 death of Freddie Gray, who died of a severe spinal-cord injury while in police custody. But there were no convictions in the case. Three of the officers were acquitted before
prosecutors dropped the charges against the remaining three in July 2016. Seen here is
Lt. Brian Rice, who was part of the bike patrol that arrested Gray. On July 18, 2016, Rice was found not guilty of involuntary manslaughter, reckless endangerment and misconduct in office in connection with Gray's arrest and death.
Officer
Caesar Goodson drove the van in which Gray was fatally injured. On June 23, Goodson
was found not guilty on all charges, including the most serious count of second-degree depraved-heart murder.
William Porter was the first of the six officers to face a trial. It
ended in a mistrial in December, and he had been scheduled to be retried before prosecutors dropped the charges against him. Porter was summoned by the van's driver to check on Gray during stops on the way to a police station. Prosecutors said Porter should have called a medic for Gray sooner than one was eventually called, and they said he also should have ensured that Gray was wearing a seat belt. Porter had been charged with involuntary manslaughter, second-degree assault, reckless endangerment and misconduct in office.
Edward Nero, one of three bike officers involved in the initial police encounter with Gray,
was found not guilty of all charges in May. He was accused of second-degree intentional assault, two counts of misconduct in office and reckless endangerment.
Garrett Miller was another one of the bike officers involved in Gray's arrest. He placed Gray in a restraining technique known as a "leg lace" before Gray was placed in the van, said Marilyn Mosby, the state's attorney for Baltimore. All charges were dropped against Miller, who had been indicted on charges of second-degree intentional assault, two counts of misconduct in office and reckless endangerment.
Sgt. Alicia White was present during one of the stops to check on Gray's condition. She and two other officers saw Gray unresponsive on the floor of the van, and when White spoke to Gray and he did not respond, she allegedly did nothing to help him, prosecutors said. All charges were dropped against White, who had been indicted on charges of involuntary manslaughter, second-degree negligent assault, misconduct in office and reckless endangerment.
Three officers were acquitted: Edward Nero, a bike officer involved in the initial police encounter with Gray; Caesar Goodson, who drove the van; and Lt. Brian Rice, the highest-ranking officer charged in connection with Gray's death.
On July 27, 2016, prosecutors dropped charges against the three remaining officers: Garrett Miller; Alicia White and William Porter.
Aside from the criminal trials, Baltimore officials approved a $6.4 million deal to settle all civil claims tied to Gray's death.
The settlement did not "represent any judgment" on the guilt or innocence of the six police officers charged, Mayor Stephanie Rawlings-Blake said.
"This settlement represents an opportunity to bring closure to the Gray family, the community and the city."
CNN's Eliott C. McLaughlin and Aaron Cooper contributed to this report.