You can feel the horror of the Florida school shooting unfold in this text exchange between two sisters

Updated 8:54 AM ET, Fri February 16, 2018

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(CNN)Facing death, 17-year-old Hannah Carbocci wanted her big sister.

A bullet had just pierced the wall of her classroom at Marjory Stoneman Douglas High School in Parkland, Florida. Gunshots -- a lot of them -- had exploded. Someone in her class was hurt. Someone else, somewhere, was yelling.
From under a teacher's desk, Hannah dialed 19-year-old Kaitlin at work.
Nothing.
So, Hannah did what teenagers do. She texted. And Kaitlin pinged back.
Hannah Carbocci, 17, left, and her sister, Kaitlin Carbocci, 19
Hannah Carbocci would not be among at least 17 people to die in Wednesday's massacre. But for several excruciating minutes, she and her sister thought she might be.
In those fragile moments, they traded 77 short text messages, which they later shared with CNN. The conversation offers an intimate glimpse into the panic, the fear and the helplessness that gripped a community that day.
On campus, students running from a madman thumbed last words of gratitude and love. Their relatives, out living ordinary days, dialed and redialed, texted and retexted, clinging to hope on their own smartphones.
Here is what Hannah, whose her sister calls her Boobles, and Kaitlin said in what they feared might be their very last exchange:
Hannah
kaitlin there is a shooter on campus
i am not joking
call 911 please
send them to douglas
Kaitlin
hannah what
are you serious rn
Hannah
kaitlin i am not joking they just shot through the walls someone in my class is injured
i am not joking
call mom and dad
i don't have service or i'd call
idk how this message is going through
Kaitlin
i'm calling
911
and then I'll call mom and dad
Hannah
please do thank you
Kaitlin
i love you so much
Hannah
im so scared i can't make any calls i love you
my phone service won't go through
Kaitlin
is police there
what's happening
hannah text me
Hannah
i don't know it's silent
i don't know if the police are here
Kaitlin
is it on lock down
Hannah
i think so
i hear yelling
Kaitlin
daddy is in response
he just called 911 they are on there way
Hannah
i am so scared kaitlin
tell them i love them so much
Kaitlin
i know Hannah
you're gonna be fine
Hannah
im so scared
Kaitlin
i know you are
daddy is on his way to the school
hannah keep texting me please
Hannah
tell them i love them so much
Kaitlin
Ii there anyone else shot
someone in your class got shot just now?
Hannah
just one person in my class room
they got shot like 8 minutes ago when the shooting started
Kaitlin
how many shots did you hear
Hannah
a lot
Kaitlin
Aad is the person ok
Hannah
the police are in the building
Kaitlin
ok how's the person who got shot
a lot of blood