>> And I remember it was pitch black in there.
>> Okay. >> Like, I could not see
inside that, that room. >> Mm-hmm.
>> It was pitch black.
(breathing slowly)
(gun firing)
>> (yelling) >> (grunts)
(radio beeps) (groaning)
>> NARRATOR: The gunman fires through the door
of one of the classrooms,
grazing Staff Sergeant Canales and Lieutenant Martinez.
>> Okay, am I bleeding?
Am I bleeding? Am I bleeding?
I started feeling, like, blood or something.
I was, like, what, I was, like, (bleep), I was shot?
What's going on? >> Mm-hmm.
>> Um, so, and Javier was, like, "Hey, I feel like," you know,
so we both kind of retreat back a little bit towards
where we (indistinct) entered. >> Mm-hmm.
>> And we kind of turned around, and we were just, like...
I thought this, I didn't know if this guy was going to come out.
>> NARRATOR: Surveillance footage shows
Lieutenant Martinez going back down the hallway alone.
Then returning to where other officers are positioned.
>> The first few moments of a response is crucial,
is what experts said.
This is the best moment in time
to engage the shooter
and rescue any victims.
So officers initially did that,
and then they stumbled back
when they're grazed by bullets.
And that ends up
really setting the stage for the rest of the response.
No one tried to go into the room
for another 70 minutes.
>> I honestly didn't think anybody was in there...
>> Mm-hmm. >> ...besides the gunman,
'cause, I, you know, I... Not that...
You know, I just honestly thought
that they were in the cafeteria,
'cause it was-- it seemed like all the lights were off,
and it seemed like it was really quiet.
I didn't hear any screaming, any yelling.
I literally didn't hear anything at all.
You know, you know... And, you know,
you would think there was,
you know, kids would be yelling and screaming.
>> Officers after officers said
that because it was so silent--
they didn't hear any screams or any indication
that a child was inside that wing--
that they believed it was empty, even though
it was the middle of a school day
on one of the last days of the semester.
>> I guess, in your mind,
did you think there was kids in that room?
>> There, I knew there was a possibility,
because it's a school,
but I didn't know for sure that
there was kids in that room, actually.
Again, it was really quiet,
and, you know, I know, you know, I mean,
I went to middle, uh, elementary school.
You know, you have your little, like,
your science class, where you walk out,
or P.E., or at different times of the day,
and hopefully, you know, other activities.
I know it was also, like, the end of the year.
So I was, like, maybe they're
doing something else, you know,
not in their classrooms,
but that was, that was
kind of wishful thinking.
"Oh, (bleep)..."
>> Children and teachers are taught to be quiet
during an active shooter threat.
That is their best defense to stay alive.
So what the children and teachers told us
and investigators is that they followed that training.
So what we found
was kind of this incredible contrast.
The children and the teachers followed their training,
but by following their training and staying quiet,
that actually meant
that officers thought they weren't there,
and it took longer for them to help them.