Riot police launch tear gas toward activists in downtown Albuquerque, following a 10-hour protest around the city on Sunday. (Russell Contreras/ AP)

large protest in downtown Albuquerque on Sunday meant to call attention to recent police-involved shootings ended with a chaotic confrontation between protesters and police. What sparked the protests? And what role did the hacking collective known as Anonymous (possibly) play? Here’s what you need to know.

The protest, which began at noon and stretched into the evening, followed two recent fatal shootings by Albuqerque police. The Albuquerque police have shot and killed 23 people since the beginning of 2010 (there have also been more than a dozen non-fatal shootings over the same span).

Two of the people shot by Albuquerque police were killed just this month, with the most recent shooting coming hours after a protest sparked by the previous one. While the police-involved shootings stretch back more than four years, it was these latest shootings — and the video footage released from one of them — that appeared to ignite these public demonstrations.

James M. Boyd was shot and killed by an Albuquerque police officer on March 16. Boyd, a 38-year-old homeless man, was shot because he was holding knives, according to Albuquerque Police Chief Gordon Eden. But police released helmet camera footage (warning: the footage is graphic) from the shooting last week that showed Boyd turning away from officers just before they opened fire.

In response to the Boyd shooting and the helmet camera footage, a video posted by a group claiming to be Anonymous called on people in Albuquerque to demonstrate on Sunday.

“It has reached a boiling point and people just can’t take it anymore,” protester Alexander Siderits, 23, told the Associated Press.

The number of fatal shootings by police in Albuquerque stands out in part because of the city’s size. In New York, for example, police killed nearly the same number of people (25) over two years (2011 and 2012) as the Albuquerque police did in four years. But New York has about 15 times as many residents as Albuquerque.

Hundreds of marchers had protested Boyd’s shooting last week, gathering in downtown Albuquerque for a protest that occurred without much police presence. Later that same day, police in Albuquerque shot and killed Alfred Redwine, 30, after saying he fired a round. Witnesses told the Albuquerque Journal that the man had held a gun to his head and never aimed it at police.

The recent shooting and the city’s police department have drawn federal attention in addition to the public outcry. The Justice Department opened a criminal investigation into the Boyd shooting, the U.S. attorney’s office for New Mexico announced Friday. And the Justice Department’s ongoing civil investigation, opened in 2012, is looking into the use of force by the city’s police department to see if it “engages in a pattern or practice of use of excessive force.”

In addition to the call for a demonstration, the video claiming to be from Anonymous also said it would target Albuquerque police Web sites. Before protesters and police faced off in the streets, the city said it was readying itself for a potential cyberattack.

Police in Albuquerque said their site had been hacked and taken offline for several hours on Sunday. The official sites for the City of Albuquerque and its police department were working on Monday afternoon, although the police department’s Facebook and Twitter pages remained down.

The Albuquerque Journal posted live updates from the protests on Sunday, documenting how the protest began quite peacefully before the confrontation between riot police and protesters eventually became physical. After protesters ignored police orders to disperse, officers threw tear gas cans at them and several protesters were arrested. Albuquerque Mayor Richard Berry later said that protesters had thrown rocks at police and said a police officer was injured, though he didn’t provide any details about the injury. At least six people were arrested.

“We respected their rights to protest, obviously, but … they’ve taken it far beyond a normal protest,” Mayor Berry said, according to the Albuquerque Journal.