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 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.
Blood will cloud and drift away, attract the murders of mermaids.
It's so cold, they all 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.
Ate their hearts, drank their blood, wash your fins in blackened mud
Now you swim, try to hide, heart beats faster from inside.
Thought it was a big charade, your life is ended by mermaids.

Murmaider (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.