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Six days before Colorado’s latest mass shooting, the suspect bought a Ruger AR-556 pistol at a gun store near his home. 

Seven days before an Arapahoe High School student killed a classmate in 2013, he picked up a 12-gauge shotgun at a Cabela’s store. 

One day before an 18-year-old allegedly obsessed with the Columbine murders caused lockdowns and closures at hundreds of Colorado schools, she purchased a pump-action shotgun just after stepping off her flight from Florida.

The Colorado Sun reviewed the state’s long history of mass shootings, school shootings and other high-profile acts of gun violence to piece together a comprehensive look at how and where the perpetrators got their weapons. 

Two main themes emerged in Colorado’s cases: In some, the guns used in the killings were purchased legally in preparation for the crimes. In others, they were stolen — such as in May 2019, when two students at STEM School Highlands Ranch used an ax and a crowbar to break into a gun safe in one of their homes, just hours before authorities say one of them shot and killed a classmate.

The Colorado cases jibe with a Federal Bureau of Investigation analysis released in 2018, which showed that in 40% of active-shooter incidents the FBI reviewed, the gunman purchased the firearm legally and “specifically for the purpose of perpetrating the attack.” About 35% of the time, the shooter had the firearms for years and had not acquired them in preparation for that attack, and in 17% of cases, the guns were borrowed or stolen. 

In some of Colorado’s older cases — such as the 2001, racially motivated killing of three people in a Rifle mobile home park — the answers are packed away in storage. The source of the weapons remains unknown, leaving gaps in the data.

Mass shootings have led Colorado lawmakers down multiple paths in an attempt to prevent them. After Columbine, the state voted to regulate sales at gun shows, and after the Aurora theater shooting, Colorado banned high-capacity magazines. Now, as the state grieves the deaths of a Boulder police officer and nine other victims of an attack at a grocery store, some state lawmakers are placing more urgency on consideration of a waiting period for gun purchases, as well as a ban on certain assault-style weapons.

Shootings that followed legal gun purchases

The gunman who killed two people at New Life Church in Colorado Springs and two others at Youth With A Mission training center in Arvada in 2007 spent several months amassing his arsenal. 

Matthew John Murray bought a Beretta .40-caliber semi-automatic handgun on Jan. 4 of that year at Sportsman’s Warehouse in Colorado Springs; a Bushmaster XM15 rifle on Jan. 9 at the Sportsman’s in Aurora; and a Springfield Armory 9mm semi-automatic handgun on Sept. 11 at Dave’s Guns in Denver, according to investigators

He also purchased $2,700 in ammunition and magazines from a website called

All the sales were legal. Murray killed himself after the Dec. 9, 2007, attack.

Similarly, in the two months before he shot 12 people to death and injured 70 others at an Aurora movie theater on July 20, 2012, James Holmes went gun shopping. 

From May 22 to July 6, 2012, Holmes purchased four guns, all legally, before the shooting during a midnight showing of a Batman movie. He made two shopping trips to Gander Mountain stores, buying a Smith and Wesson .223 semi-automatic rifle in Thornton and a .40-caliber Glock pistol in Aurora. He also bought a second .40-caliber Glock handgun and a Remington 870 shotgun at Bass Pro Shops in Denver, according to court documents.

Holmes shopped online for bullets, high-capacity ammunition magazines and body armor, purchasing some of the items from

In response to that mass shooting, Colorado lawmakers in 2013 passed new regulations requiring background checks for every gun purchase and transfer, and they limited ammunition magazines to 15 rounds. 

The same year the background check law was passed, Arapahoe High School student Karl Pierson bought a 12-gauge pump-action shotgun for $229.99 from a Cabela’s sporting goods store in Lone Tree a week before he shot his classmate, 17-year-old Claire Davis, and then killed himself inside the Littleton high school. 

Pierson wrote in his diary several days before the shooting that he had purchased the shotgun and “Mom does not know about it,” according to records released in the case. 

The sale was legal because he was 18 years old and he passed the background check. He brought the gun, along with 124 rounds of ammunition, three Molotov cocktails and a machete into the school on Dec. 13, 2013.

Three of the four guns used in the 1999 attack at Columbine High School were purchased legally at the time, through unregulated sales at a gun show. The teen killers bought a fourth gun illegally from a 22-year-old man they met through a mutual acquaintance. 

A girlfriend of one of the Columbine gunmen, who killed 12 classmates and a teacher on April 20, 1999, bought a 12-gauge pump-action shotgun and a 12-gauge double-barreled shotgun, along with a 9mm semiautomatic carbine, at the Tanner Gun Show. She was 18, while Eric Harris and Dylan Klebold were both 17.

Eric Harris wrote about the purchase in his diary in late November, about four and a half months before the shooting. 

In another transaction, the teens bought a TEC-DC9 semi-automatic handgun in a private sale arranged by one of their coworkers at Blackjack Pizza. The same man, who was later convicted of selling a handgun to a minor, sold the boys 100 rounds of ammunition the day before the mass shooting. 

In 2000, Colorado voters closed the “gun-show loophole,” passing a ballot measure that required background checks for prospective buyers at gun shows. The state also banned straw purchases, making it illegal to buy a gun on behalf of someone else who is not allowed to have a gun.

Twenty years after Columbine, almost to the day, an 18-year-old student from Surfside, Florida, who authorities said was infatuated with the Colorado school shooting, set off a statewide panic. Although Sol Pais was too young to buy a gun under Florida law, she was able to purchase a shotgun in Colorado. 

Immediately after landing at Denver International Airport, she drove to Colorado Gun Broker near Columbine High School and bought a pump-action shotgun and ammunition, according to authorities. She passed a background check and walked out with the gun. 

At the end of the two-day saga, after schools up and down the Front Range were shut down and anxious parents kept their kids away from parks and playgrounds, Pais was found dead. She had killed herself alone in the woods, at the base of Mount Evans. 

Florida law prohibits gun sales to people under 21 and requires a three-day waiting period. 

Shootings with stolen weapons

The two STEM High School students accused of shooting at their classmates on May 7, 2019, killing 18-year-old Kendrick Castillo and wounding eight others, were too young to purchase handguns in Colorado. 

Instead, they used an ax and a crowbar to bust into a safe at one of their homes after they could not find the key, according to an arrest affidavit. Devon Erickson and Alec McKinney broke into the safe in Erickson’s mother’s closet, according to the document. Erickson’s father kept the key with him, the court record states.

Inside the safe, they found a Glock 21 .45-caliber semi-automatic pistol, a Beretta M9 9mm semi-automatic pistol, a .357 Magnum Taurus Revolver and a Ruger 10/22 .22-caliber semi-automatic rifle, as well as ammunition. They hid the guns in backpacks and a guitar case that same day and carried them into their Highlands Ranch school. 

Deer Creek Middle School in Littleton has been the site of two shootings — and in both cases, the gunman took the weapon from a relative. 

In 1982, a 14-year-old student shot and killed a classmate with a .38-caliber revolver, taken from the home of the 14-year-old’s grandfather four days before the shooting.

In 2010, a 32-year-old man took a bolt-action rifle from his father and opened fire on students at the school just as classes were dismissed for the day. Two students were wounded before the gunman was tackled by a math teacher.

One in five Colorado high school students believe they could easily get a handgun, according to a University of Colorado study published in March. The study, from the Anschutz Medical Campus and the Colorado School of Public Health, examined data from more than 46,000 students. 

“There is not a lot of data out there to compare this to, but just from a gut-check standpoint, it seems like a lot of teens at least perceive they have access to a handgun,” said lead author Ashley Brooks-Russell, an assistant professor in the Colorado School of Public Health. 

“They might be thinking of a friend’s home or a relative’s home.” 

Shootings in which gun details weren’t released 

In several cases reviewed by The Sun, details about how the perpetrator obtained the guns used in mass shootings were not readily available. The most common reason is that the gunman died the day of the shooting or was sent to a mental institution for treatment before all the details of a case were publicly revealed in a trial.

The documents from the criminal investigation into a 2001, racially motivated shooting of three people in a Rifle mobile home park are contained in 17 boxes moved off-site of the Garfield County Courthouse, making them not readily available, for example. The gunman, who was sent to the state mental health facility in Pueblo, used a .38-caliber revolver as he walked into the mobile home park and began shooting his victims, all of whom were Latino, according to news reports. 

Twenty years later, no one currently at the Garfield County District Attorney’s Office worked that case or recalls how the man obtained the gun. 

Eagles Nest Armory gun shop seen on March 24, 2021, in Arvada. The suspect in the King Soopers shooting purchased a firearm there six days before the shooting. (Hugh Carey, Special to The Colorado Sun)

Similarly, there is no public documentation describing how the gunman accused in the 2015 shooting at a Colorado Springs Planned Parenthood got his guns. The shooter had four SKS rifles, five handguns, two other rifles, a shotgun and 500 rounds of ammunition, and propane tanks, according to an arrest affidavit. Four people were killed. He is now at the state mental hospital. 

A shooting in downtown Colorado Springs just a month earlier, on Halloween 2015, involved three guns, all legally purchased in 2009. Noah Harpham, who had bipolar disorder and whose parents were making a plan to have him hospitalized, had a DPMS AR-15 rifle, a .357 Magnum revolver and a 9mm pistol, according to court records. Investigators found a receipt for the revolver, which Harpham had purchased from Paradise Sales in Colorado Springs. 

The gunman was killed in a shootout with police officers after he fatally shot a male bicyclist and two women, seemingly at random. 

The man who killed 16-year-old Emily Keyes, a student at Platte Canyon High School, in 2006 brought multiple guns the day he barged into the Bailey high school and held six female students hostage. Duane Morrison used a Glock 22 .40-caliber semi-automatic pistol and, after killing Keyes, killed himself. Law enforcement records say he was known to have possessed 15 firearms, including two purchased for him by a nephew and one by a niece in the years before the school shooting. Why Morrison had relatives buy the guns or where he obtained the rest of them was unknown.

The man who killed three people in a Thornton Walmart in 2017 used a 9mm Luger handgun, but public records do not describe where or how he got it. An arrest affidavit says Scott Ostrem pulled the handgun from his black jacket and began firing at random in the store. 

Gun laws being discussed in Colorado

Colorado lawmakers are discussing a handful of gun-related measures this year, including a not-yet-introduced bill that would require a waiting period to buy a gun. 

One bill would require gun owners to safely store their weapons and another would require people to let authorities know if their guns were lost or stolen

Lawmakers point toward the killing last year of 21-year-old Isabella Thallas, who was shot to death with an AK-47-style rifle that the suspect allegedly stole from a Denver police sergeant, according to 9News. The gun wasn’t reported missing until after the officer realized it may have been used in a crime.

Democrats in the statehouse have discussed running a bill banning certain assault-style weapons, and have said they might push legislation requiring a waiting period between when a person tries to buy a gun and is able to take home the weapon. Halfway through the current legislative session, neither has been introduced.

Ten states and the District of Columbia have waiting periods that apply to the purchase of guns, according to the Giffords Law Center to Prevent Gun Violence. Colorado lawmakers pushing for a waiting period cite not only mass shootings, but the 2016 case of a Highlands Ranch mom who shot her two young boys and killed herself hours after buying a gun. 

In 2019, Colorado lawmakers passed a “red flag” law that allows judges to order the temporary seizure of firearms from a person considered a significant risk to themselves or others. The law is intended to allow family members to have the guns removed from relatives with severe mental health issues.

Danika WorthingtonSocial and Presentation Editor

Danika Worthington is the Social and Presentation Editor for The Colorado Sun. She manages social media, newsletters, graphics and design. Previously, she was a digital strategist at The Know for The Denver Post, and a breaking and general assignment reporter before that. In...

Eric Lubbers

Eric Lubbers is the Chief Technology Officer and one of the co-founders of The Colorado Sun. A native of Yuma, Colorado, he writes The Sunriser newsletter in addition to handling most of the behind-the-scenes tech stuff. Email:

Jennifer Brown

Jen is a co-founder and reporter at The Sun, where she writes about mental health, child welfare and social justice issues. Her first journalism job was at The Hungry Horse News in her home state of...