An arrogant crime scene cleaner and her impressionable partner/best friend begin a messy murder spree to provide the work that’ll save their business from going under.

Mike:

Thanks for the link to the murder-com article. Now that I've had time to think it over -- and tweak my daily dosage of Zoloft -- I can see comedic possibilities.

However, I would like to suggest that while the easy-to-manipulate side kick may be necessary for the plot, it's not needed for the logline. More important -- good point Vivien -- is the need to include the antagonist.

So maybe something like:

A steep decline in murders drives a crime scene cleaner to begin a messy murder spree to stay in business while staying one step ahead of the homicide detective investigating the crime scenes.
(33 words)

fwiw

Dpg, two dark comedy of this nature come to my mind:
- Delicatessen (a cannibal butcher and landlord)
- In Bruge (two ruthless professional hit men)

I can see the absurbity of your story. You'd need flawless execution to make a film about two serial killers funny.

I can think of two films of this genre: Delicatessen (a cannibal butcher) and In Bruge (two professional hit men).

As for the logline, it's well written and most of the elements are there. What missing is the antagonist. You mentioned in your comments that the impressionable partner would become the antagonist later on. You want to incorporate this item into the logline. Without it, the story has no conflict, and when there is no conflict there is no story.

You may say something like:
'An arrogant crime scene cleaner and her impressionable partner and best friend go on a messy murder spree to provide the work that'll save their business from going under until the partner [make a decision that threatens their operation].