Another unarmed black teen was shot and killed by a police officer near Pittsburgh last week, setting off days of angry protests, heightened racial tensions, and recriminations regarding law enforcement's use of deadly force.

Antwon Rose Jr., 17, was the 490th person shot and killed by police officers in 2018, according to a database maintained by the Washington Post. So far this year, there have been 27 more killings by police than during the same period last year. At least five other people were shot and killed by police nationwide since Rose was gunned down.

The increase in deadly shootings underscores the need for police departments to rethink their culture and training.

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Rose and another passenger fled from a car stopped by police who suspected they were involved in a shooting minutes before. Cellphone video showed Rose being shot in the back three times. The officer who shot Rose was sworn in 90 minutes before the incident, but had previous law enforcement experience.

Rose's killing echoed police shootings across the country, including Michael Brown, the 18-year-old shot and killed in Ferguson, Mo., in 2014; Tamir Rice, 12, who was shot and killed in 2014 by Cleveland police responding to a report of a man waving a gun; and Jeremy McDole, the 28-year-old who was sitting in a wheelchair when he was shot and killed by several officers in Wilmington in 2015.

To be sure, each shooting has a different set of circumstances, complicated by split-second decisions made amid tense situations. But cellphone video from the incidents also makes it difficult to explain the need for police officers to shoot unarmed suspects.

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And there is no denying this fact: Police across the United States shoot and kill way more people than police in any other developed country. For example, police in the U.S. shot and killed more people in 24 days than police in England and Wales did in 24 years, according to a 2015 report. Even after accounting for the difference in population, the number of killings by police in the U.S. far exceeds other countries.

After the shooting of Brown in Ferguson, a group called Campaign Zero examined the use of force policies in 99 of the 100 largest police departments in the U.S. The group developed eight common-sense reforms aimed at ending killings. They include requiring officers to de-escalate situations before resorting to force; restricting choke holds; and prohibiting officers from shooting at moving vehicles.

The group found that not one department implemented all eight of the polices. To its credit, the Philadelphia Police Department requires most of the policies recommended by Campaign Zero.

But even that has not ended the unnecessary use of deadly force. A year ago, a Philadelphia police officer shot and killed a suspect who dropped a gun and ran away with his hands in the air. The officer was fired but, like many other officers who kill suspects, he has not been charged.

Sound policies are needed, but regular training, strong leadership and accountability are needed to change the culture in many police departments where use of deadly force is all too routine.