Police science is one of the youngest and most rapidly growing professions in the United States today. I have revised this handbook for fans of Frank and Joe Hardy who are interested in learning about modern police practices. The first seven chapters, based upon true stories from police files, illustrate how Frank and Joe use the various facets of police technology while tracking down criminals. Further uses of these techniques -- fingerprinting, surveillance, and other related skills in the science of criminal investigation -- are detailed in the last five chapters. William F. Flynn, FBI Special Agent who recently retired, acted as my consultant in the preparation of this revised edition. It is our sincere hope that many readers of this handbook will someday join the ranks of our country's brave and dedicated law-enforcement officers who fight the never-ending war against crime. - Foreword.