A 25-year-old woman's Snapchat video captured the initial gunfire inside the Pulse nightclub in Orlando.
Amanda Alvear was at Pulse with a group of friends and on Snapchat when the gunshots erupted.
She looks into the camera then looks away confused. That's where the video ends.
A friend, who Buzzfeed identified as Mykol Marte, posted that video to Facebook.
"Found out thru snapchat my friend Amanda Alvear was there at Pulse last night," Marte wrote. "Tried calling and texting and still haven't gotten a reply."
The video has been viewed over a million times since it was posted Sunday afternoon.
Marte took to Facebook again on Monday after learning that Alvear had died. He wrote in part: "You're here today and in a snap you could be gone tomorrow. Right now my heart is filled with such great sorrow."