The importance of co-convictions in predicting dangerous recidivism: blackmail and kidnapping as a demonstration study

Co-convictions are court convictions made at the same time as a more serious conviction. Their importance has been little recognized.We investigate their value using data on two separate serious crimes. Taking official conviction careers in England and Wales (1979—2001) for blackmail (n = 5774) and kidnapping offenders (n = 7291), we considered how much information on co-convictions is normally overlooked, and how knowledge of co-convictions contributes to predicting serious recidivism. We identified that co-convictions were pervasive, with 54 per cent of convictions for blackmail and 77 per cent for kidnapping having co-convictions. Co-convictions provided extra explanatory power in predicting the risk of a subsequent sexual or violent offence for both blackmail and kidnapping. For blackmail, most types of co-conviction were associated with a significantly raised relative risk, whereas for kidnapping, only co-convictions which were not acquisitive, sexual or violent had a significantly raised relative risk. We concluded that co-convictions are a useful measure of short-term specialization and are important when predicting serious recidivism.