Colorado's tragic and prolific history of mass shootings from Columbine to King Soopers

For many in Colorado, hearing the news Monday of 10 people being shot dead at a Boulder grocery was a tragic, but familiar headline.

Colorado, a state where open carry is legal, has suffered through some of the most deadly mass shootings in American history, including the 1999 Columbine shooting and the Aurora theater attack in 2012, which have fundamentally changed safety measures in modern day America.

The Monday attack come less than a week after eight people were killed in a shooting spree at three Atlanta-area spas.

Heated debates over gun laws have been reignited in the U.S.

The Giffords Law Center, a Colorado-based gun control group co-founded by former Congresswoman Gabrielle Giffords, gives the state a scorecard grade of C+ for overall gun safety.

While Colorado now has universal background checks, a large-capacity magazine ban and state database background checks, advocates say the state is missing assault weapon restrictions, waiting periods, open carry regulations and gun owner licensing.

King Soopers -- March 2021

In the Monday attack, 21-year-old alleged gunman Ahmad Al Aliwi Alissa, of Arvada, Colorado, opened fire at the King Soopers grocery store in Boulder at about 2:40 p.m., killing 10.

Police officer Eric Talley, 51, was the first law enforcement officer to arrive at the scene and was fatally shot. The other victims were identified Tuesday as Denny Stong, 20; Neven Stanisic, 23; Rikki Olds, 25; Tralona Bartkowiak, 49; Suzanne Fountain, 59; Teri Leiker, 51; Kevin Mahoney, 61; Lynn Murray, 62; and Jody Waters, 65.

The suspected gunman suffered a leg wound in crossfire with police and was taken into custody.

He has been charged with 10 counts of murder, Boulder Police Chief Maris Herold said. A motive is not known at this time.

STEM School Highlands Ranch -- May 2019

Two suspects stormed the STEM School in Highlands Ranch, a K-12 charter school, armed with handguns and weapons hidden in guitar cases and opened fire in two separate locations of the school on May 7, 2019.

One student was killed and eight others were injured.

Teenagers Alec McKinney and Devon Erickson, 16 and 18 years old respectively, were arrested for the fatal shooting. They were students at the school.

McKinney pleaded guilty and was sentenced to life in prison, while Erickson, who pleaded not guilty, has had his trial delayed several times. It is now expected to begin in May.

Kendrick Castillo, an 18-year-old who tried to confront the shooters, was killed in the attack.

Planned Parenthood -- November 2015

Three people were killed and nine were injured on Nov. 27, 2015, when gunman Robert Lewis Dear Jr. opened fire in a Planned Parenthood clinic in Colorado Springs.

In the harrowing attack, a police officer and two civilians were killed and five officers and four civilians were wounded. After storming the clinic, Dear engaged in an hourslong standoff with police.

Dear faced 68 counts in the federal case, including use of a firearm during a crime resulting in death and violating a law ensuring access to clinic entrances.

In several courtroom outbursts, Dear declared he was guilty and shared anti-abortion sentiments and called himself a "warrior for babies," per The Associated Press.

In May 2016, a judge residing over his case ruled that Dear was incompetent to stand trial and ordered him indefinitely confined to a Colorado state mental hospital, where he remains.

Aurora theater -- July 2012

A midnight screening of the film "The Dark Knight Rises" turned into a massacre when gunman James Eagan Holmes stormed into a Century 16 movie theater in Aurora on July 20, 2012.

He was dressed in tactical clothing and set off tear gas grenades and shot into the audience with several firearms.

In total, 12 people were killed and 70 were injured. Fifty-eight of those were wounded from the gunfire, while the rest were injured while fleeing the massacre.

In the 60 days leading up to the shooting, Holmes had purchased four guns from local shops and more than 6,000 rounds of ammunition, police said at the time. All of the weapons and ammunition were purchased legally, police said.

He was sentenced to life in prison without the possibility of parole on Aug. 7, 2015.

Columbine High School massacre -- April 1999

The horrific Columbine High School massacre unfolded on April 20, 1999, in Littleton and remains one of the most infamous mass murders in U.S. history.

In the attack, senior students Eric Harris and Dylan Klebold murdered 12 students and one teacher before taking their own lives. A total of 21 people were wounded.

For years the shooting was burned into Americans memories as the deadliest school shooting in US history. The attack inspired several copycat assaults.

The gunmen plotted the attack for a year with hopes of carrying out the deadliest shooting in U.S. history.

The shooting led to increased school security efforts and sparked national debates over gun control as well as high school bullying, internet use and violence in video games and movies.

Gun control advocates call for reform

In Monday's shooting, the suspected gunman used a Ruger AR-556 pistol purchased on March 16, according to the arrest warrant affidavit.

The shooting came just 10 days after a judge blocked a ban on assault rifles that Boulder passed in 2018.

Currently, Colorado is an open carry state with some exceptions. The city of Denver generally bans the open carry of firearms. Colorado also does not impose waiting periods between the purchase of a firearm and the transfer of the firearm to the customer, per Giffords.

Colorado Ceasefire, a major gun reform group in the state, is calling for Congress to pass a ban on assault weapons and a law to require universal background checks.

For many in Colorado, entire generations of young people have had their lives marred by fear and trauma of mass shootings.

"Five years before I was born, two shooters walked into Columbine High School and opened fire, killing 13," Jayla Hemphill, a volunteer with Colorado Students Demand Action, told ABC News. "I'm now 17, and yesterday a man walked into the Table Mesa King Sooper and did the same, killing 10. The gun violence epidemic has lasted the span of my entire life, and there has not once been significant federal action to end it."

Frank DeAngelis, who served as principal at Columbine at the time of the 1999 shooting, urged for legislators to push gun reform in the wake of the attack.

"Different events, but the feelings are the same," DeAngelis said to the Denver Post. "We've seen this happen in Colorado way too many ways."

Giffords, who was shot in the head in an assassination attempt in January 2011, told ABC News in a statement, "It's been 10 years, and countless American communities have had to face something similar ... It's beyond time for our leaders to take action."