In 2006, McCray's team went to explore the planet Sorth and found a reactor facility that was leaking radiation. While they were checking out the facility, they were attacked by the Genii. Tanaka helped cover Dr. Radek Zelenka as he figured out what was wrong with the power plant.
Soon after, Zelenka was separated from the squad and tried to contact Tanaka over the radio but got no response. Tanaka, along with the rest of his team were killed.
The Genii Subcommander Argan Loci took one of their radios and acted like he was a member of the team looking for him, to learn of Radek's location. Radek asked if he was Tanaka, which Argan proceeded to pretend to be, but Radek noticed his voice didn't have Tanaka's accent. He also pointedly called McCray the wrong name and asked him what his own first name was. When Argan failed both these tests, Zelenka knew Argan wasn't Tanaka, because he knew Tanaka would know both their names. (SGA: "Meltdown")