Machines and processes include the computer, fingerprint systems, and surveillance aids. Laboratory techniques include bloodstain analysis, the use of chemical information for intelligence purposes, and study of the strategy of analysis. Application of the scientific attitude in the investigation of crime itself can occur if recognition exists of the close similarities between the investigation of a difficult major crime and the experimental investigation of a difficult research problem in the laboratory. One way to ease the investigator's task is to define a numerical scale against which an investigator who has interrogated a witness may be able to measure a judgment of the interview. The Yorkshire Ripper case is presented to illustrate both the use and the need for the use of science in crime investigation.