DNA Testing & its Admissibility
Deoxyribonucleic acid (DNA) testing, also referred to as genetic fingerprinting, is a powerful technology used by prosecutors to identify criminal suspects and may be used in robbery, attempted murder and homicide cases. Every person, with the exception of an identical twin, possesses a unique DNA structure which scientists use for identification of a person, much like fingerprints are used for identification. The probability of two individuals sharing the same DNA pattern is less than one in 30 billion under ideal testing conditions. DNA testing thus provides a virtually certain positive identification, unlike conventional methods which utilize blood or serum tests.
DNA samples may be chemically isolated from dried or fresh blood stains, body tissues, semen stains, hair roots and buccal swabs (scrapings of the inner mouth lining). The amount of DNA which is sufficient to perform a DNA test varies depending on the specific biological sample used. An insufficient sample renders the test unreadable and produces no identification; thus, there is no possibility of falsely incriminating an innocent suspect or exculpating a guilty one.
DNA samples recovered during a criminal investigation may suffer from exposure to the environment which could potentially affect the reliability of the testing. Furthermore, because the procedure is new, expensive and complicated, DNA tests have been used in only a few criminal cases in the United States.
In People v. Castro, 144 Misc.2d 956, 545 N.Y.S.2d 985 (1989), the court concluded that the techniques used in DNA analysis are generally accepted in the scientific community and therefore DNA test results may be admissible into evidence under the Frye standard. The defendant was charged with two counts of murder and the prosecution sought to introduce evidence of DNA identification tests which purportedly indicated a match between DNA from a bloodstain found on the defendant's watch with the DNA of the victim. Because the testing laboratory failed to perform the accepted scientific techniques and experiments in several aspects, the court ruled that the DNA evidence demonstrating an inclusion was inadmissible as a matter of law. The court allowed, however, the DNA evidence of exclusion of the defendant as the source of the blood on the watch. The court also made several pre-trial hearing procedural suggestions, including: serving notice of intent to offer DNA evidence as soon as practicable; giving discovery to the adversary; and requiring the proponent to have the burden of going forward to establish that the tests and calculations were properly conducted.