The four usual sources
Homeowner or renter insurance
Some policies treat cleaning after a death or an injury as part of a covered loss, and some do not. The only way to know is to ask your agent or insurer what your policy says, before work begins if you can. California's Department of Public Health gives the same advice on its list of registered companies. Keep the written price, any photographs and the invoice.
The state, after a crime
The California Victim Compensation Board lists crime scene clean-up among the expenses it can reimburse. The rules are narrow, and they are set out further down this page.
The landlord
In a rental, the building belongs to the landlord, so work on the unit is normally the landlord's to arrange and pay for, often through the property's insurance. The tenant's belongings are a separate matter.
The estate
Where the person who died owned the home, cleaning is normally one of the costs of settling the estate. Whoever is handling the estate can hire the company and keep the invoice with the other bills. If you are unsure you have authority to sign, ask a probate attorney first.
Two things people ask
Should I wait for the insurer before cleaning starts?
Phone the insurer first and ask. Some want to see the room, or photographs of it, before anything is taken out. If waiting is making the home unlivable, tell them so, and ask what they need for the work to begin.
Will the cleanup company bill my insurer?
Some companies send their invoice to the insurer, and some expect you to pay and be paid back. Ask the company how it works. Whether a claim is paid is always the insurer's decision.