(CNN) - Once again, gunfire erupted in a Colorado school, this time leaving one student dead and eight others wounded.
Tuesday's carnage at STEM School Highlands Ranch occurred miles from Columbine High School, yet another in a litany of tragedy -- two decades removed -- in which two students opened fire on classmates, killing 12 of them and a teacher.
"If you had suggested to anyone behind me, or in this room, that in 20 years in 20 miles we would have dealt with Columbine, Aurora theater, Arapahoe High School, the shooting of Zack Parrish and four other deputies, we'd have thought you mad, yet here we are again," District Attorney George Brauchler lamented Wednesday.
He added, "This does not define us, it won't today, and it won't tomorrow. These are abhorrent acts. Problem is when you get three, four or five of them within a 20-mile radius you begin to think they are less abhorrent. But I'm here to tell you, this is not who we are."
This is what Colorado has endured in two decades:
The April 20, 1999, shooting changed the way police responded to all the active shootings that followed.
Nearly 50 minutes passed after the gunfire started before SWAT teams entered the school in Littleton.
By then, 12 students and one teacher were slaughtered by Dylan Klebold, 17, and Eric Harris, 18.
The shooters made home videos before the attack with references to what they were going to do and apologizing to their parents for their actions. They then killed themselves.
The shooting at Columbine -- about 7 miles from the scene of Tuesday's slaughter -- ranked as one of the worst mass shootings in US history as well as one of the deadliest episodes of school violence.
A gunman opened fire July 20, 2012, at a movie theater in Aurora, killing 12 people and injuring 70 others.
The shooting occurred 18 minutes into the midnight showing of "The Dark Knight Rises" at the Century Aurora 16 multiplex theater.
Authorities said the shooter was "dressed head-to-toe in protective gear" -- a ballistic helmet, protective gear for his legs, throat and groin, black gloves and a gas mask. He propped open a door before throwing tear gas canisters into the theater. After the canisters exploded, witnesses said he started shooting, first at the ceiling and then at the crowd.
He used an AR-15 rifle, a 12-gauge shotgun and at least one of two .40-caliber handguns police recovered at the scene.
On July 16, 2015, James Holmes was found guilty on all 165 counts against him in connection with the massacre: 24 first-degree murder, 140 attempted murder and one count of possession or control of an explosive or incendiary device. He was sentenced to life in prison without parole.
Brauchler led his prosecution.
An 18-year-old student walked into Arapahoe High School in Centennial, armed with a pump-action shotgun, a machete and a backpack containing three Molotov cocktails, a bandolier of ammunition across his chest.
Claire Davis, a 17-year-old senior, was fatally shot once in the head December 13, 2013, as the shooter fired randomly into school hallways.
Police said the shooter was looking for revenge against a librarian but couldn't find the faculty member and killed himself as a school resource officer moved in.
The shooting happened about 10 miles from Columbine High.
Sheriff's deputy fatally shot, 4 law enforcement officers wounded
On New Year's Eve 2017, five law enforcement officers were shot and one of them died after a barricaded suspect opened fire at an apartment complex in the suburb of Highlands Ranch, about 20 miles south of Denver.
Two civilians also were shot, and the suspect was shot and killed later by police, according to Douglas County Sheriff Tony Spurlock.
Deputy Zackari Parrish, 29, was killed.
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