Watching developments closely is event organizer Miguel Lopez, who's having difficulty getting around the better part of two days since the startling incident.
That's because he was knocked to the ground and nearly trampled during the chaos that followed the gunfire.
Lopez was on stage when lead started flying, and at first, "we didn't know what was going on.... We didn't even hear the gunshots. We just saw smoke and dust come up in the air, and then people just scattered or went to the ground."
Before long, Lopez continues, "they broke through three barricades.... So I tried to reach my number two guy, and I was trying to stream across the crowd to call the duty officer when I was pushed to the ground.
"The security crew pulled me out just in time, before the crowd trampled over me."
He's still sore from the incident, and very emotional. "There are a lot of people who are probably going to need some therapy" after what they witnessed, he says, fighting back tears.
Three people were injured in the shooting, with two suffering leg wounds and a third being grazed by a bullet. But the situation could have been a lot worse -- and he believes the reason more people weren't seriously hurt to proper preparation.
"We took out terrorism insurance this year, after we did our planning with the Office of Emergency Management," he notes. "And then, last week, Boston happened" -- a reference to the bombing at the Boston Marathon -- "and my heart just dropped. It was a big eye opener."
Even before the tragic events in Boston, Lopez had already decided to increase security in anticipation of a larger crowd following the passage of Amendment 64. "There were more Denver police officers and more of our own security. Last year, we had just two of our guards on the stage, and we increased that to six. And the security marshals went from fifteen to thirty."
Did more people attend as well? The Denver Police Department leaves crowd estimates to event organizers, and given everything that happened, Lopez admits that he hasn't had a chance to analyze aerial photos and come up with a figure. He thinks as many as 75,000 people may have come and gone throughout the day, while other observers guess that the crowd on hand from 4:20 p.m. to just after 5 p.m., when the shooting took place, was in the 10,000-15,000 range.
In the aftermath of the shooting, Lopez has been happily surprised that the reporting has largely avoided casting blame for what happened on either marijuana or hip-hop -- Lil' Flip was performing when shots were fired. And he feels that's appropriate. He references the City Park Jazz festival shooting of last year, when Officer Celena Hollis was killed in a random shooting; earlier this month, Rollin Oliver pleaded guilty to second-degree murder in the incident. "This can happen anywhere," he stresses. "It had nothing to do with the rally. Obviously, it was crazy individuals doing something in the middle of tens of thousands of people.
"If this was gang-related, we have to remind ourselves what actually started gangs in the first place," he goes on. "We've always known that alcohol prohibition created gangs, and marijuana prohibition has done the same thing."
After the shooting, day two of the festival was canceled "out of respect for the victims," Lopez says. "It wouldn't have been ethical or moral for us to continue these celebrations after what happened to them." At the same time, though, he says the individual who fired the shots violated the First Amendment rights of everyone involved with the rally, even if the incident was a random act of violence rather than an attempt to silence those who wanted to speak about making marijuana legal in all circumstances, not just under the limitations of Amendment 64.
Does Lopez fear that locals and visitors alike will be reluctant to attend next year's 4/20 rally because of what happened in 2013? "I don't think Americans in general let themselves live in fear," he maintains. "We've always heard throughout the generations that the only thing we have to fear is fear itself, and we're so thankful for that lesson."
In his view, the event prior to the shooting had been one of the best ever, and he was especially pleased by cooperation with the Denver Police Department; he sees the DPD's actions before and afterward as symbolic of an improved relationship that he hopes will continue to grow.
"Our thoughts and feelings go out to all those affected, and particularly those who were wounded," he adds. But he also knows many people will be working through their experiences in the days and months to come -- and that includes him.
Here are more photos from the scene, followed by additional images and videos.
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More from our Follow That Story archive: "Rollin Oliver pleads guilty to second-degree murder in slaying of Officer Celena Hollis."