Derek was a member of the Mars Resistance and the Anla'Shok.
After months of being interrogated about her experience with Kosh, Lyta Alexander escaped Psi Corps custody and began working with the Martian Resistance. While in hiding with the resistance, Alexander learned of the Psi Corps sleeper program. Finding out that one of these sleepers was on Babylon 5, she discovered the password required to unlock this hidden personality and traveled to Babylon 5.
Derek was able to smuggle the information to Lyta, after Lee got the information to him.[1]