Alvares was a member of the Homeguard.
Ivanova and Sinclair put on a ruse that he is secretly bitter and hateful towards aliens and fellow member of Homeguard, Malcolm Biggs, buys it completely. Biggs reveals Alvares and the other Homeguard agents on board Babylon 5 as well as a new stealth cloaking field. Sinclair and Ivanova reveal the double cross as Garibaldi and his team arrest Alvares and his fellow Homeguard members.[1]