Does Expert Witness Have to Know All the Facts of the Case ?

An expert witness need not have personal knowledge of all the facts on which he bases an opinion. Instead, an expert may base an opinion or inference on facts or data perceived by, reviewed by, or made known to him before testifying. See Tex. R. Evid. 602, 703. A qualified expert may testify to scientific, technical, or other specialized knowledge if the trial court determines that such testimony will assist the trier of fact to understand the evidence or determine a fact in issue. See Tex. R. Evid. 702. The proponent of scientific or technical evidence has the burden of demonstrating by clear and convincing evidence that the evidence is both reliable and relevant. See Kelly v. State, 824 S.W.2d 568, 573 (Tex. Crim. App. 1992); see also Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 590-92, 125 L. Ed. 2d 469, 113 S. Ct. 2786 (1993). Three criteria must be satisfied for scientific evidence to be considered reliable: (1) the underlying theory must be valid; (2) the technique applying the theory must be valid; (3) the technique must be properly applied on the occasion in question. See Kelly, 824 S.W.2d at 573. Kelly applies to all scientific evidence offered under rule 702, including intoxilyzer test results. See Hartman v. State, 946 S.W.2d 60, 63 (Tex. Crim. App. 1997).