Anderson Cooper anchors "AC360" from Aurora, Colorado, scene of the deadly movie theater shooting, tonight 8 p.m. and 10 p.m. ET on CNN.
(CNN) -- The posts show how quickly life can change.
"Everyones dressing up as Batman, im going dressed as Bruce Wayne... Albeit a short stubby unsexy Bruce Wayne #CouldntFindBatmanMaskInTime," wrote one Twitter user, identified online as Zach Eastman.
"Going to see the final batman tonight! So EXCITED!!!" wrote another Twitter user, @DjaylaRene.
And, in hindsight, most chillingly: "Of course we're seeing Dark Knight ... people should never argue with me."
Those posts surfaced before the shootings early Friday morning at a late-night showing in Aurora, Colorado, of the Batman movie "The Dark Knight Rises," in which 12 people were killed and dozens more were injured. All three people who were quoted above appear to have been in the theater complex when a heavily armed gunman opened fire on moviegoers, according to police.
The third post appears to be from Jessica Ghawi, who was reported dead in the shooting. Ghawi was a former sports-news intern at a television station in San Antonio, according to that station, Fox 29. "It's true, my former intern Jessica Ghawi was a victim in the shootings last night. She used @JessicaRedfield as her twitter handle," wrote a Twitter user identified as Mike Taylor.
In the hours after the shooting, her friend mourned her death in real time.
"Devastated," wrote a sports radio host in Denver, identified online as Peter Burns. "Lost a very close friend in the shooting last night. @JessicaRedfield came to Denver to pursue sports career. I'm shaking."
The horrifying posts highlight a shift in the way our society tells the story of a tragedy, and also how we react to it. Before Twitter, smartphones and YouTube, it would have been impossible for an event like Colorado's "Batman Massacre" to have played out for the global public in real time.
The shooting is just the latest instance of social media being used to document a tragedy or a news event even as it is unfolding. A Pakistani man last year unwittingly live-tweeted the raid that killed Osama bin Laden. And the war in Syria is being documented in large part by citizens and members of the opposition movement who risk their lives to post YouTube videos and photos of the violence.
But the social media posts about the Colorado shooting are a haunting reminder of the visceral power of first-person accounts of tragedy. And also a sign that society these days deals with grieving after an event like this in a much more public and immediate way than in years past.
Reports of the 1999 Columbine school shooting, for example, which happened only 17 miles from Aurora, spread in a much different way. Thirteen years ago, witnesses talked to TV crews rather than uploading their stories instantly to the Internet with mobile phones.
Some reports from the Aurora movie theater appeared to come out as the shooting occurred.
"Now I'm thinking it was bullets coming through the wall from 9 causing smoke and fire cracker sounds. #aurorashooting #batman #shootng," a Twitter user identified as Jamie Marshall wrote.
"Never seen so many cop cars in my life. Its a parade of lights," wrote Isaac Ramos.
"Everything keeps replaying in my head. It was so unreal," @DjaylaRene wrote.
"I am getting ready to cry. So scared. I need a hug. I almost got shot 9 times. I had a chance to be like 50," wrote another Twitter user, @Abenistar.
He later added: "I seen a person bleeding out their mouth and gasping for their last breath. This ain't right. #Century16Shooting. Thunk the world is ending."
Shaky YouTube videos show people screaming, crying and rushing out of the theater after the shooting, some of them with bloody wounds. Another video, apparently taken outside the building by a person who was in the theater next to the shooting, offers a glimpse into the mindset of a person who has just witnessed tragedy. The amateur videographer sounds to be at a loss for words.
"Oh Jesus. July 20th, 2012. Aurora Century 16," he says, in a sort of real-time confessional about the event. "There has been a massive shooting here. A lot of people wounded, a lot of people dead. I can't really take pictures, just because I'd rather (be) helping people than wanting to take pictures of some pretty ghastly (expletive). There's some guy in a gas mask apparently -- teargassed theater 9. We were in theater 8. Just lit it up. It hit a lot of people, a lot of younger people. Oh. It's pretty -- it's pretty bad."
Officials also turned to the Internet in an effort to make sense of the events.
The Red Cross is asking people who witnessed the shooting to tell loved ones that they were OK over social media sites like Facebook and Twitter.
"People don't know how close you were, so help alleviate that anxiety," spokeswoman Patricia Billinger told USA Today.
And other officials used the Internet to offer sympathy.
"We certainly appreciate the nation's thoughts and prayers as our police department continues to investigate the terrible theater shooting tragedy that occurred today," the city of Aurora wrote on its Facebook page. "Our condolences go out to the victims and their family members."
CNN's Doug Gross and Dorrine Mendoza contributed to this report.