All criminal networks are social networks with multiple channels of communication and collaboration between their members. In this paper, we analyze different types of criminal networks with respect to metrics commonly used in social network analysis literature. We focus mostly on two types of networks: cocaine trading and terrorist activities. We also include a legal organization's network for comparison. Our findings reveal that there are significant differences in terms of some of these metrics between different types of criminal networks. These differences, in turn, may help security forces to identify unknown networks or substructures in very large networks as potential criminal networks.