H.B. No. 688 amends the Code of Criminal Procedure to establish that a defendant with an intellectual disability cannot be sentenced to death for a capital offense. The bill introduces Chapter 46D, which outlines definitions related to intellectual disability, including "deficits in adaptive behavior," "developmental period," and "significantly subaverage general intellectual functioning." It also sets forth procedures for determining whether a defendant is a person with an intellectual disability, including the appointment of a disinterested expert to evaluate the defendant and the requirement for a jury to determine the defendant's status unless waived.

Additionally, the bill specifies that the burden of proof lies with the defendant to demonstrate their intellectual disability by a preponderance of the evidence. The state may present evidence to rebut the defendant's claims. The changes made by this Act will apply only to trials commencing on or after its effective date of September 1, 2025, regardless of when the alleged offense occurred.