There are no fingerprints deep under water, nothing to tie one to a crime.

And if you seek vengeance, all you need are instruments of pain.

You need your:

Knives? Check.
Rope? Check.
Dagger? Check.
Chains? Check.
Locks? Check.
Laser Beams? Check.
Acid? Check.
Body Bag? Check.

Murmaider
[x16]

But beware!
For when you quench your blood thirst, others will seek their vengeance on you, and they won't rest until you're dead.

They'll have their:

Shiv? Check.
Pipe? Check.
Hammer? Check.
Axe? Check.
Subject? Check.
Location? Check.
Desire? Check.
Vengeance? Check.

Hold your breath, swim and strain - the smell of death, can't escape.
Underground I tried to murder, tried to murder some mermaids.
It's so cold, they don't know what you've done, you can't run.
Vengeance is below for thee, thousand leagues below the sea.
You've been tracked, you've been seen murdering the next of kin.
In their homes (you) drank their blood, wash your face in blackened blood.
Now you swim, try to hide, heart beats faster from inside.
thought it was a big charade, your life is ended by mermaids.

Mermaider
[x16]

Swords? Check.
Saws? Check.
Clubs? Check.
Claws? Check.
Hatred? Check.
Anger? Check.
Mermaid? Check.
Murder? Check.

MURDER! MURDER! MERMAID! MURDER!

Your life was ended by mermaids.