A number of killings of unarmed black men by white police officers in recent months have sparked protests across the US, with protesters alleging racism in police forces and raising accusations that officers use excessive force.
Officers have rarely been charged in the shootings, even when the incidents were recorded.
The killing of unarmed black teen Michael Brown in Ferguson, Missouri was a catalyst for a recent surge in protests in the country.
A jury in November chose not to charge a local police officer for the shooting.
The US Justice Department has conducted investigations into a number of police departments after shootings and unearthed damning evidence that officers in Ferguson targeted black residents.
The report led to the resignation of Ferguson's police chief Thomas Jackson in March of this year.
In December, a grand jury in New York City chose not to charge a white police officer who killed an unarmed black man with a chokehold.
Eric Garner, a father-of-six, was illegally selling cigarettes on 17 July 2014 when police officers tackled him and put him in a chokehold.
The decision not to charge police officer Daniel Pantaleo sparked a number of protests.
In March, police in Los Angeles shot and killed a homeless man during a confrontation on a city street.
Officials said the officers encountered the man while responding to a robbery call, with local media quoting officers as saying the man was resisting arrest and tried to grab one of the officers weapons.
Video of the incident was posted online and showed the officers scuffling with the man, with several shots fired while the man is on the ground.
Days later, police in Wisconsin shot and killed a black teenager who was apparently unarmed.
The officer, who was responding to a disturbance, entered an apartment which Anthony 'Tony' Robinson was reported to have entered.
Madison Police Chief Mike Koval said that a struggle ensued and the 19-year-old was fatally shot.
Initial investigations did not find a weapon at the scene and an out-of-area investigation was ordered.
