This document proposes a method called Statistical-based Detection of Black hole and Grey hole attackers (SDBG) to detect both individual and colluding attacks in delay tolerant networks (DTNs). SDBG works by having a trusted authority monitor nodes' behavior based on their encounter records, message records, and forwarding histories. It aims to improve detection accuracy and reduce the impact of false positives compared to existing detection methods. The methodology involves network and authority creation, route finding and data forwarding, and detecting colluding attacks based on monitoring nodes' interactions and messages. Simulation results show SDBG can effectively detect attacks with varying drop rates even under collusion with high accuracy and low false positives.