(a) A district or county attorney, either before or after the case is tried and finally determined, may not take from any person a fee, article of value, compensation, reward, or gift, or a promise of any of these, to prosecute a case that he is required by law to prosecute or as consideration or a testimonial for his services in a case that he is required by law to prosecute.
(b) Section 41.004(a) does not apply to funds provided by the government of the United States through the Texas Department of Human Services to local prosecutorial offices for the purpose of assisting to defray the costs of prosecutions.