According to the official police report, at approximately 12:39 a.m. local time, an armed gunman "appeared" at the front of one of the theaters screening The Dark Knight Rises. The suspect threw some sort of explosive into the crowd and started shooting.
Attendees at the theater immediately turned to Twitter to share information with friends and loved ones. One user waiting in line outside the theater captured video of the immediate aftermath of the chaos and uploaded it to YouTube.
In the hours following the tragedy, members of the media, friends and witnesses used Twitter, Instagram and Facebook to share information about the situation, give updates on the status of loved ones and express their condolences.
After the suspect, 24-year-old James Holmes, was identified, other James Holmeses in Colorado took to the web to make the disassociation clear.
You can see the timeline as it unfolded online below.
[View the story "Mass Shooting at Batman Premiere in Colorado" on Storify]
Stephanie Haberman created the Storify for this story.