Funding. Several factors may have contributed to this increased use of scientific evidence. At one time there was substantial funding for "forensic" science research—the application of science in a legal setting. The creation of the Law Enforcement Assistance Administration (LEAA) in 1968 undoubtedly played a significant role. In the 1970s the LEAA underwrote a number of research projects designed to encourage the forensic application of scientific knowledge, and the development of some techniques can be traced directly to this research. Voiceprint analysis is the most prominent example. Other funded projects dealt with blood analysis, blood flight characteristics (blood spatter evidence), trace metal detection, and the polygraph. Later, the F.B.I. spent considerable resources refining the forensic application of DNA, and the Bureau of Alcohol, Tobacco, and Firearms joined the F.B.I. in establishing computerized firearms comparison systems.
Supreme Court decisions. Some commentators attribute the expanded use of scientific evidence to another factor, namely, U.S. Supreme Court decisions of the 1960s, in which the Warren Court severely restricted the acquisition of evidence for criminal cases by traditional crime-solving techniques such as interrogations and lineups. There is some suggestion in the Supreme Court's own cases that the Court deliberately encouraged greater reliance on scientific techniques. For example, in one case the Court wrote: "Modern community living requires modern scientific methods of crime detection lest the public go unprotected" (Breithaupt v. Abram, 352 U.S. 432, 439 (1957)). In Escobedo the Court observed: "We have learned the lesson of history, ancient and modern, that a system of criminal law enforcement which comes to depend on the 'confession' will, in the long run, be less reliable and more subject to abuses than a system which depends on extrinsic evidence independently secured through skillful investigation" (Escobedo v. Illinois, 378 U.S. 478, 488–89 (1964)).
Interestingly, at the same time the Court was erecting constitutional barriers to the use of confessions and lineups, it was removing Fourth and Fifth Amendment obstacles to the use of scientific evidence. The most important case was Schmerber v. California, 384 U.S. 757 (1966). The Court, in an opinion by Justice Brennan, held that the privilege against compulsory self-incrimination applies only to testimonial evidence and not to physical evidence. Thus, the police could extract blood from Schmerber for blood-alcohol analysis without violating the Fifth Amendment privilege. This ruling had broader significance; the ruling also meant that handwriting exemplars, fingerprints, voice exemplars, and, later, biological samples for DNA testing could be compelled from a suspect without running afoul of the self-incrimination clause. Justice Brennan likewise authored Warden v. Hayden, 387 U.S. 294 (1967), in which the Supreme Court overruled its prior cases prohibiting the seizure of "mere evidence." Under the "mere evidence" rule the police could seize only contraband, instrumentalities of a crime, or fruits of a crime. Most scientific evidence, such as blood, hair, gunshot residues, and blood-stained clothing, would have been "mere evidence" and hence immune from seizure.
Technology. It is unclear that either of these reasons—research funding or Supreme Court decisions—fully explains the increased use of scientific evidence. The answer may be more basic. It is simply expectable that a society so dependent on science and technology should turn to such knowledge as a method of proof. With computer technology running modern businesses, magnetic resonance imaging (MRI) aiding medicine, and Nintendo and other electronic devices captivating children, no one should be surprised to see DNA evidence in the courtroom.