New York City, United States - Cynthia Howell is angry. Eleven years ago, her aunt was killed after police tossed a concussion grenade into her apartment during a mistaken drug raid.

On Saturday, she was at the vanguard of a march in Manhattan over fears of racism in an overly-militarised police force.

"Enough is enough. This country cannot still allow these same police practices and let cops get away with it," Howell told Al Jazeera. "We love our loved ones as much as they love the ones they go home to. It's not just an issue of black or white, it's about abuse of authority."

Howell's aunt, Alberta Spruill, was a prime example of bad policing. The 57-year-old long-time city government worker died from a heart attack in 2003 after a stun grenade was thrown into her home in West Harlem, a mostly black neighbourhood of New York.

This so-called "no-knock" approach, used to surprise criminals, followed police receiving faulty information about drugs and guns at Spruill's address. Her death has been overshadowed by more recent examples of police killings of blacks that drew protesters onto the streets on Saturday.

Sadly, police brutality didn't begin or end with the deaths of Michael or Eric. Policing the black community has not changed substantially since the 1700s.

- Marsha Coleman-Adebayo, protest organiser

Rallies followed controversial grand jury decisions to not prosecute white lawmen in the high-profile deaths of two unarmed black men - Michael Brown and Eric Garner - in unrelated cases that have stoked fears of excessively violent and racially biased policing. 

The Millions March NYC and other protests were staged "for all those killed by racist killer cops", organisers said. An online publicity drive asserted that #BlackLivesMatter and marchers shouted slogans linked to the deaths of Brown and Garner.

Chokehold

Garner, 43, an overweight street peddler selling untaxed cigarettes, died from a chokehold by Officer Daniel Pantaleo in New York on July 19. A mobile phone video of the heavy-handed arrest and Garner's last words - "I can't breathe" - went viral on the internet.

Brown, 18, was shot and killed by Officer Darren Wilson while walking down a backstreet in Ferguson, Missouri, on August 9. Wilson described being punched by a 130kg brute; a witness said Brown was gunned down with his hands raised in surrender pose.

There is plenty of evidence that blacks get the rough end of the law. They make up 13 percent of the US population, but are victims of 26 percent of police shootings, according to the Centre on Juvenile and Criminal Justice. Blacks are shot by police at 2.8 times the rate of white non-Latinos.

Incarceration rates paint a bleaker picture. The National Association for the Advancement of Colored People (NAACP) says blacks make up nearly 1 million of the US' 2.3 million detainees - meaning blacks are jailed at nearly six times the rate of whites.

Despite guarantees of legal equality under the US Constitution, many African Americans live in mostly black neighbourhoods with higher crime rates, less-stable households of single mothers, and bad job prospects. Zero-tolerance school policies and tough sentences for drug-related crimes trap many young black men into a criminal cycle from which it is difficult to escape, the NAACP says.

Against this backdrop, only 37 percent of blacks have confidence in the police, compared to 59 percent of whites, according to combined Gallup polls.

"Sadly, police brutality didn't begin or end with the deaths of Michael or Eric," Marsha Coleman-Adebayo, an academic and protest organiser, told Al Jazeera. "Policing the black community has not changed substantially since the 1700s: surveilling black communities, apprehending black men and bringing them to a discrete form of violence; once lynching but nowadays mass-incarceration."

An officer with his assault rifle in Oakland, California [Reuters]

The UN High Commissioner for Human Rights, Zeid Raad Al Hussein said he was "deeply concerned" by the "disproportionate" number of blacks behind bars as well as those who die at the hands of police. Other UN experts called for probes into police prejudice.

Taking action

The US government has taken action. President Barack Obama announced a $75m plan to help police units buy body cameras and record interactions with the public; the Department of Justice (DOJ) launched civil rights probes into the Ferguson and New York deaths.

Another DOJ investigation this month found that Cleveland police had used excessive force in November, when officers in the city shot dead a 12-year-old boy who was carrying what turned out to be a toy gun.

Advocates for police say that single tragedies do not tell the whole story. In reality, the number of blacks who end up in jail or shot dead is roughly proportionate to the number of interactions that take place between policemen and African Americans, they say.

"There's an overlap with race, but class and poverty play into it," William Terrill, a former officer and criminologist at Michigan State University, told Al Jazeera. "Police look at geographic space, good areas and bad areas with high crime rates. 

"When they do that, irrespective of race, you're more likely to be subject to police oversight in those areas."

Studies of these "hot spots" began in the 1990s and found in such cities as Minneapolis, 3 percent of addresses accounted for half of all crime calls to police. High rates of incarceration and police killings among blacks are functions of crime rates in impoverished districts - not police racism, said Terrill.

"Some people honestly believe that cops don't shoot white people and don't give tickets to white people for minor issues. This view is demonstrably false," Peter Moskos, a former Baltimore lawman and academic at John Jay College of Criminal Justice, told Al Jazeera. "Let's get the facts right and then talk about injustice - because there's plenty out there, but police provide an easy scapegoat."

The high-profile deaths of Brown, Garner, and 28-year-old Akai Gurley - who was accidentally shot and killed by a rookie officer in Brooklyn on November 20 - ignite simmering racial tensions that are more about jobs, schooling and inequality than police racism, said Moskos.

"We can't make a data set out of individual incidents. To say it's all the fault of racist cops is letting the system off the hook," added Moskos.

Growing wealth gap

Widespread anger over the killings fits into a narrative of deep-rooted racism in the US that stretches back to the slavery-era, through a civil rights struggle, and up to Obama's election as the country's first black president six years ago.

A study this week by Pew Research Centre found the wealth of white households was 13 times the average of black households in 2013 - the highest economic gap to have existed between the two communities since 1989.

While protesters and criminologists interpret the data differently, there is a shared concern over how militarised American police have become - a gripe of demonstrators at Ferguson's rallies, who faced off against armoured vehicles and lawmen toting assault rifles.

One study by Eastern Kentucky University's School of Justice Studies found that Special Weapons and Tactics (Swat) teams have been increasingly deployed from about 3,000 times in 1980 to about 50,000 times annually nowadays.

"You don't tend to see armoured personnel carriers patrolling the streets of wealthy white areas of American cities," David Sklansky, a former federal prosecutor and academic at Stanford Law School, told Al Jazeera.

Whether the issue is perceptions of police racism among African Americans - or the reality - it is a problem either way, added Sklansky. "Lack of trust affects their interaction with the police, and the ability of the police to get community help in doing their job."

Follow James Reinl on Twitter: @jamesreinl

Source: Al Jazeera