Controversial killings by police

So far in 2016, more than 500 people in the U.S. have been shot and killed by police, according to data compiled by the Washington Post. While only a fraction of those deaths are considered questionable, the recent killings of black men in Louisiana and Minnesota have once again reignited a national debate about law enforcement tactics and race in America.

Here's a look back at some of the most controversial police-involved deaths in recent years.

Alton Sterling: Baton Rouge, La.

On July 5, 2016, police confronted Alton Sterling outside a convenience store after receiving a call saying he'd threatened someone with a gun. Cellphone videos show Sterling, who possessed a gun but didn't appear to be brandishing it at the time, being pinned down by two officers before being shot and killed. "You [expletive] move, I swear to God," said one officer. Footage of the incident flooded the media and caused outrage nationwide. The U.S. Justice Department is investigating the incident.

Philando Castile: Falcon Heights, Minn.

On July 6, 2016, Philando Castile was shot in his vehicle after being pulled over at a traffic stop. According to his girlfriend, Diamond Reynolds, who began live-streaming video on Facebook just after he was shot, Castile told the officer he had a concealed weapon, along with a permit for it. As he was reaching for his wallet, he was shot, she said. Video shows the officer continuing to point a gun at Castile even as he slumps over bleeding. The incident sparked a furor and demonstrations nationwide.

Jamar Clark: Minneapolis

In November 2015, Jamar Clark was shot in a confrontation with the police, who'd been called in after paramedics said he was interfering with treatment of an assault victim. Accounts of the incident differ: some protesters said he was handcuffed at the time of the shooting, though forensic experts said he wasn't handcuffed and had his hand on an officer's gun. His death set off weeks of protests in Minneapolis. The two officers involved in the incident faced no charges.

Jeremy Mardis: Marksville, La.

In November 2015, 6-year-old Jeremy Mardis was shot five times as two deputy city marshals pursued his father. His father had previously fled an attempt to serve a warrant but is shown holding his hands up in footage of the incident. The child, who was autistic, was shot in the head and chest. Both marshals, Derrick Stafford and Norris Greenhouse Jr., were charged with second-degree murder.

Samuel DuBose: Cincinnati

In July 2015, Samuel DuBose was shot by a University of Cincinnati police officer who stopped his car for missing a front license plate. The officer's body camera captured footage of shooting. Demonstrations took place at the local courthouse soon after, demanding justice for DuBose's family. The officer, Ray Tensing, was fired and charged with murder and voluntary manslaughter; he has pleaded not guilty.

DuBose's family reached a $5.3 million settlement with the university.

Freddie Gray: Baltimore

In April 2015, police arrested Freddie Gray "without force or incident," according to his arrest report. Police said he was carrying an illegal switchblade at the time, though prosecutors have said the knife was legal. He was placed in the back of a police van, but was not properly seat belted, and sustained critical neck and spine injuries during the subsequent ride. According to Baltimore State's Attorney, Gray indicated that he needed medical attention several times but was denied immediate assistance. He died of his injuries five days later.

Freddie Gray: National outcry

The incident sparked a national outcry and debate about police brutality toward black people and minorities. Thousands gathered in cities around the country to protest Gray's death, in some cases shutting down roads and clashing with police. So far, three of the officers have been tried, with two being acquitted and one ending in mistrial. The latter case will be retried and trials of three other officers are still pending.

Walter Scott: Charleston, SC

In April 2015, Walter Scott was shot eight times in the back by a policeman while fleeing from a traffic stop. He was unarmed at the time. The officer, Michael Slager, has been charged with murder in the shooting.

Tony Robinson: Madison, Wisc.

In March 2015, 19-year-old Tony Robinson, who was black, was shot and killed in his apartment by white police officer Matt Kenny, who'd responded to calls about a disturbance. Robinson, who was unarmed at the time, was shot after he knocked Kenny down with a blow to the head, police said.

Robinson's death sparked protests over the string of incidences in which unarmed black men were shot by white officers. Kenny did not face criminal charges.

Anthony Hill: Decatur, Ga.

In March 2015, Anthony Hill, a mentally ill veteran, was shot and killed during what his family described as a psychiatric episode in which he stripped naked. Robert Olsen, the officer responding to the call, said he'd gotten reports of a man behaving erratically and when he got to the scene, Hill lunged at him. Witnesses say Hill was unarmed at the time. His girlfriend said Hill suffered from bi-polar disorder and had been experiencing PTSD after his deployment to Afghanistan. Olsen has since been indicted for felony murder and pleaded not guilty.

Laquan McDonald: Chicago

In an October 2014 encounter with the police, 17-year-old Laquan McDonald was shot 16 times. He was carrying a knife and police accounts allege he'd lunged at an officer. However, video footage released more than a year later shows McDonald walking away from police when they began shooting. The shooting continues even after McDonald had fallen to the ground. The event set off protests in Chicago and prompted a deeper investigation of police culture in the city. Jason Van Dyke, the officer who shot McDonald, has been charged with murder.

Tamir Rice: Cleveland

In November 2014, 12-year-old Tamir Rice was shot outside the Cudell Recreation Center while drawing what turned out to be a pellet gun. He died the following day. According to Cuyahoga County Prosecutor Tim McGinty, it was "indisputable" that the boy was pulling the toy gun from his waistband, either to hand it to police or show them that it was a toy, but it was impossible for police to know that. Protesters took to the streets of Cleveland and New York following the event. The officer who shot Rice will not face criminal charges.

This photos shows images from the night of the event.

Michael Brown: Ferguson, Mo.

In August 2014, 18-year-old Michael Brown was shot and killed by police while walking on a street near his home. He was unarmed at the time. News of his death sparked national outrage and days of protests in the St. Louis suburb of Ferguson, where police used rubber bullets and tear gas to disperse the masses. Protests got so unruly that the Missouri National Guard was deployed. The incident fueled the national Black Lives Matter movement, calling for an end to police brutality against the black community.

Michael Brown: Ferguson, Mo.

Following Brown's death, the FBI opened an inquiry into the shooting. Darren Wilson, the officer who shot Brown, was not charged.

The Department of Justice conducted its own investigation, discovering clear patterns of discrimination within the Ferguson justice system.

Eric Garner: New York

In July 2014, Eric Garner died while being arrested for illegally selling cigarettes. Police said Garner died of a heart attack, but footage of the incident showed police putting Garner in a chokehold while he repeatedly said, "I can't breathe." The officer was not indicted.

The incident sparked outrage and fueled the Black Lives Matter movement with "I can't breathe" becoming one of its slogans.

James Boyd: Albuquerque

In March 2014, a graphic video showing police shooting James Boyd, a homeless black man, in Albuquerque surfaced. Police said Boyd was carrying knives and threatened officers, but footage of the incident shows him turning away before they began shooting. The video prompted hundreds of online responses and a protest in the city.

Kelly Thomas: Santa Ana, Calif.

In July 2011, Kelly Thomas, a homeless man diagnosed with schizophrenia, was beaten to death by six officers after failing to follow their commands. The incident was recorded by a surveillance camera, sparking controversy about police handling of the mentally ill. The city of Fullerton settled the case in November 2015, with Thomas' father receiving a $4.9 million settlement.

Oscar Grant: Oakland, Calif.

In January 2009, 22-year-old Oscar Grant was pulled off the BART train by transit police after a reported fight, thrown on the ground and shot. Grant was unarmed. Witnesses recorded the incident on their cellphones and the event caused an outcry in the city. Johannes Mehserle, the officer who shot Grant, was convicted of involuntary manslaughter, admitting he intended to fire his Taser, not his gun. He served less than a year in jail. A film based on the shooting, Fruitvale Station, came out in 2013.

Sean Bell: New York

In 2006, Sean Bell was leaving a strip club with his friends after his bachelor party when police officers shot his car 50 times, thinking one of the men had been armed. None of them were. Bell became a symbol of police brutality against the black community. The officers involved were acquitted of all charges, including one of manslaughter.

Bell is pictured here with his fiancee, who he was scheduled to marry just hours after the shooting.

Amadou Diallo: New York

In February 1999, New York police shot Amadou Diallo 41 times on the stoop of his building, having mistakenly thought that he was carrying a gun. He was simply holding his wallet. The four officers involved in the shooting were acquitted of charges including second-degree murder, criminally negligent homicide and reckless endangerment of bystanders.