If the debtor has differents contracts from city and county of los angeles, do you think I can go to served the city and county with my writ of execution papers? And do you think either one of them will release the money to me as a creditor? Thanks.

If you are certain the defendant in your suit and the contractor in the city and county are the same (because it must be the same entity, not the same man 'behind' two separate corporations), you could serve the city and county with garnishment papers, provided this is allowed by state law. A 'writ of execution', as I understand the term, is a document commanding the sheriff to seize all property of the defendant; if this is what your document says, then contact the sheriff's department for an explanation of what its procedure is to handle the paperwork.