Speaker verification systems require some kind of background model to reliably perform the verification task. Several algorithms have been proposed for the selection of cohort models to form a background model. This paper proposes a new cohort selection method called the Close Impostor Clustering (CIC). The new method is shown to outperform several other methods in a text-dependent verification task. Several normalization methods are also compared. With three cohort models and the best score-normalization method, the CIC yielded an average Equal Error Rate (EER) of 0.8%, while the second best method (Maximally-Spread Close, MSC) yielded average EER of 1.1%.