Brandon Tomlinson works for Genentech in South San Francisco, California. Genentech manufactures Human Growth Hormone (HGH), a performance enhancing drug. HGH increases muscle mass by stimulating protein synthesis, strengthen bones by stimulating bone growth and reduce body fat by stimulating the breakdown of fat cells. HGH is popular among some athletes because it's impossible to test for. Brandon apparently has done presentations at conferences on the problem of undetectable performance enhancing drugs in athletics.
Brandon's brother Lance Tomlinson owns the Max Muscle Sports Nutrition franchise store in San Jose, California. Brandon's Sports Nutrition Store sells supplements for body builders.
DEA agents knew that Lance's Sports Nutrition shop also sold HGH that was stolen from Genentech. It didn't take much effort for them discover that Lance had a brother who worked at Genentech. They connected the dots and made the arrests.
What a couple of geniuses. If you're gonna steal from your employer, don't use your brother as a fence.