According to a 2003 survey conducted by Skogan and Frydl, criminal investigation is one of the least studied topics in police research. This article presents some of the findings of an examination of 153 homicide files opened between 1990 and 2001 by a large police force in Quebec. The paper is divided in four parts: (1) First, a brief survey of the writings on criminal investigations is conducted; (2) Our research project is then described and some of the methodological difficulties encountered are discussed; (3) A categorization of the main types of criminal investigation is developed, revealing an unsuspected diversity among investigations; (4) Finally, empirical findings are presented, focusing on the time needed to clear a homicide case, on the main determinants of the clearance process, and on the role of forensics and expertise in solving cases.