Link analysis has been an important tool in crime investigation. Explicit or implicit social links, such as kinship, financial exchange, telephone connection, links derived from modus operandi, time of day, and geographic relationship, are often used to construct links between criminals. This paper proposes an association model based on modus operandi mining to establish links among crime cases and chronic criminals. Two data sets of robbery and residential burglary crime records were collected from a local police department and were used for experiment to evaluate the performance of the proposed approach. Explicit social links (12), such as friendship, kinship, financial exchange, sexual relationships, and telephone connections, are often used to construct social network among suspects and victims in crime investigations. Although implicit crime links, such as links derived from modus operandi, geographic relationship, and crime time of day, are valuable and oftenly used in crime profiling, the effectiveness of their usage is mainly depending on the interpretation and expertise of an investigator. While social link analysis of solved crime cases could be based solely on explicit links, associations among unsolved ones can only be constructed by implicit links derived from mining crime databases. According to Locard's Exchange Principle: every contact of the perpetrators of a crime scene leaves a trace;the perpetrators will both bring something into the scene and leave with something from the scene(13). Furthermore, the type、quantity、position、and status of evidences left at a crime scene often provides clues for crime reconstruction (5). By analyzing evidences left at a crime scene, a criminal profiling specialist can derive the information needed to reconstruct a crime and narrow down the suspects (10). Criminal profiling is mainly based on 'method of operations' or modus operandi, such as preparation actions, crime methods and weapon(s), etc. It has been shown that after a criminal gets used to a certain method of operation, he/she will use the same modus operandi again in committing other cases (6). Therefore, modus operandi information not only can be used to identify the relationship between suspects and crime cases, but also to discover the association among unsolved cases (11). In Taiwan, the final step of crime investigation procedure is to file a report for each case. Besides essential case data, such as case category, location, time of a day, suspect's and victim's names, a crime record also includes five modus operandi variables, namely crime cause(CC), crime habit(CH), preparation action(PA), crime method(CM), and crime tool(CT). Each modus operandi variable has a set of predefined values for selection in report filing. This paper proposes an association model based on modus operandi mining to construct links among crime cases and chronic criminals. Two local police data sets of 1504 robbery cases and 5443 residential burglary cases were collected and used for experiment to evaluate the proposed approach. The organization of this paper is as follows: section 2 gives related literatures, section 3 describes the proposed model, section 4 presents the experimental results, and section 5 gives conclusions of this paper.