Recent advances in tracking technology enable the gathering of spatio-temporal data in the form of trajectories. Analyzing trajectories can convey knowledge useful for prominent applications and designing computational solutions for mining groups of moving objects may turn out to be a valuable means for a wide class of problems related to mobility. The task of group mining has been investigated by considering mostly the spatial closeness and similarity of the trajectories, while little attention has been paid to the relationships between the trajectories and time-changing nature of the trajectories. The relationships may provide evidence of interactions between the moving objects. The time-changing nature may provide evidence of dynamics of the movements. Therefore, interactions and dynamics can be sources of information that one can consider to discover new forms of groups. In fact, groups of objects may be of interest not only when the objects move together or move close from each other, but also when they come from different places, change direction, join together and then move away from each other. Motivated by this, we introduce the concept of crews and propose a computational solution to discover crews. A crew gathers moving objects with similar interactions and similar dynamics. The proposed computational solution relies on i) new movement parameters, which explicitly consider interactions and dynamics, and ii) a distance-free clustering algorithm, which groups objects based on the similarity of the movement parameters. We conduct extensive experiments on real-world trajectory data, present a quantitative evaluation of the quality of the crews and perform comparisons with a baseline algorithm and with an algorithm of group pattern mining. The empirical results provide interesting insights on the relevance of some parameters in the construction of the crews.