Washington: When New York Police Department cops choked Eric Garner to death last year after they found him selling loose cigarettes in contravention of the tax code, a passer-by captured it all on a camera phone.

"I can't breathe," Mr Garner kept saying. "I can't breathe." He said it 11 times as he died in a chokehold.

When an Oklahoma reserve sheriff's deputy shot Eric Courtney Harris dead at the beginning of this month after he'd been tackled fleeing an arrest, he said in a voice redolent with shock and fear, "Oh, God. Oh, he shot me; I didn't do shit!"

And then: "I'm losing my breath."

To which an officer responds, "F--- your breath."

Mr Harris died an hour later.

It now seems impossible not to link the killings and the words. Garner's dying words, "I can't breathe!" became a protest chant through the long northern hemisphere autumn and winter of protests across the United States against the killings of unarmed black men and youths by white cops.

Now in the northern spring it is as though a cop has responded.

"F--- your breath."

All of the recent killings have had their own shocking quirks. A few stand out. Tamir Rice was just 12, playing with in a park with a dangerous-looking toy gun when an officer shot him dead within two seconds of arriving on the scene. The cop didn't even get out of the car.

Michael Brown was unarmed and already shot once in the hand when he turned and began to approach officer Darren Wilson, who fearing for his life shot him dead.

Levar Jones, 35, was driving through Columbia, South Carolina when a highway patrol officer pulled him over for an alleged seatbelt violation and demanded to see his licence. When Mr Jones turned to retrieve it, the officer fired four times, hitting Jones in the hip.

"Why did you shoot me?" Mr Jones, who survived the shooting, asked the cop. The officer's lawyer would later explain that Mr Jones had reached for his licence "aggressively".

In South Carolina last week Walter Scott was shot at least eight times. We don't know what he said as he died, but we know that he was unarmed, running from a cop and shot in the back.

There are several common themes to these stories. The dead are black and the cops are white. The officers are commonly – though not always – absolved of any wrongdoing. The most recent killing to hit the news, the shooting in Oklahoma, stands out not only by the apparent callousness displayed by at least one officer after the shooting, but by the sheer preposterousness of it all.

The volunteer deputy who pulled the trigger, mistaking his Taser for his gun, was Robert Bates, a wealthy insurance executive with, apparently, a fondness for crime fighting in his spare time.

"Oh, I shot him. I'm sorry," Mr Bates said after pulling the trigger. He was cleared by an internal investigation.

Those who defend police point out that the long-term trend of police shootings is coming down in line with overall crime rates. That might be the case, but since no national figures are kept we don't know exactly how many people American police shoot and in what circumstances they do it.

It is also clear that due to the prevalence of guns in America officers are right to fear that anyone they confront on the street might be armed with a lethal weapon.

As tensions between police and the police increased over the past months, at least four officers have been shot, in what might have been retaliatory attacks. Two were killed execution-style as they sat in a car in New York, two were wounded by a sniper in Ferguson during protests over Mike Brown's murder.

But another commonality is that in all these cases the shootings were filmed, and that is why they are being discussed.

Video cameras – be they worn by police, carried in phones or installed as security – are now ubiquitous.

Their presence means that police shootings that might have been ignored by media are now being the focus of growing outrage.

And this could explain why on Monday, a day after the Eric Harris video was released, part-time deputy Bates was charged with second degree manslaughter.

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