Data were collected from criminal justice operations at three sites between November 1973 and July 1974: Contra Costa County, Calif.; Dade County, Fla.; and Columbus, Ohio. Following a discussion of the role of physical evidence in the decision to prosecute, the report examines the prosecutor's use of crime laboratory analyses in the pretrial processes and in preparing a defense. The study found that only a small fraction of reported offenses that involved physical evidence examination entered adjudication and few of these went to trial. However, this is a national trend regardless of whether physical evidence is examined. Data on guilty pleas indicated that physical evidence information increased the ratio of guilty pleas as charged to guilty pleas to a reduced charge. The study concluded that the role of physical evidence in adjudication was primarily corroborative, and court records did not contain sufficient information to judge if attorneys preferred physical evidence to eyewitness testimony. Also reviewed are judge and jury perceptions of the role of physical evidence, the criminalist's viewpoint, and the need for training prosecutors about physical evidence. The report emphasizes that communications should be improved between prosecutors and criminalists. Charts, tables, a glossary, and 12 references are appended. See NCJ 83270, 83272, and 83272 for Vols. 1, 3, and 4.