On all Hallows Eve, a single mother becomes the target of a terrifying attack.

There's a woman on the ground and somebody in a full Halloween costume holding a shotgun, aiming it down at her.

This isn't a Halloween prank. This is a real murder.

And two of the only witnesses are the victim's twin daughters.

They both had blood all love their costume and in their hair and on their face.

It put me in a place of resolve.

I'm going to make sure that we find out who did this.

The investigation uncovers evidence of a dangerous love triangle.

There is a history of violent behaviors that's often a trigger for an escalation.

I knew it wasn't her that did the killing, but I knew she's involved somehow.

What happened? Give it all to me and let me help you.

I was afraid from my life. We walked away going, she's not telling us the truth.

But the monster demands control.

As sick and twisted as it is, I think that was his ultimate vengeance.

They face a real-life boogeyman.

The October 31st, 2015.

It's a typical hectic Halloween in the town of Brandon, Florida, a suburb just east of Tampa.

There's a lot of families, so Halloween is a time that would be very busy in the Brandon area.

You usually see groups of parents with their kids walking the neighborhood, going door-to-door,

trick-a-treating.

After handing out candy at her apartment complex all evening, a young woman is relaxing on her couch with a horror movie marathon.

But around 11 p.m., she gets a different kind of scare.

...