Orlando Mass Shooting Victim's Snapchat Captured Start of Gun Battle

6/13/2016 6:55 AM PDT

Orlando Mass Shooting: Victim's Snapchat Captured Start of Gun Battle

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One of Omar Mateen's victims was posting videos to social media at the moment he fought his way into the club and opened fire.

25-year-old Amanda Alvear recorded several Snapchat clips from inside Pulse Nightclub -- most of them are innocent fun with friends.

But in the final video Amanda was recording herself when more than a dozen shots are heard.

Many survivors have said clubgoers initially thought the shots were part of the music DJs were playing -- so they didn't react immediately. You can see in Amanda's video -- obtained by the Daily Mirror -- she was not panicked at first by the gunfire. 

Amanda was killed during the standoff. Her sister commented on the video ... "I'm so heartbroken. You could make anyone's day with the smile of yours."