Kirby was arrested shortly after the March 11, 2009 crash in Newport Beach, California, registering a .13 blood/alcohol level, well above the legal limit.
According to the Orange County Register, prosecutor Jason Baez told jurors in his opening statement that skid marks show that Kirby was driving at speeds over 100 mph when he lost control of his car and crashed into Lewis.
Baez also acknowledged that while Lewis may have been racing with Kirby, the crash would not have occurred without Kirby's negligence.
The prosecution contends that Kirby was responsible for the Jamboree Road collision that sent Lewis' Ferrari into a concrete light pole, where it split in half. The 45-year-old Lewis was later pronounced dead on the scene.
Kirby is facing several legal charges aside from vehicular manslaughter for his role in the crash, including driving under the influence causing bodily injury as well as fleeing the scene and causing great bodily injury to multiple victims (Lewis' girlfriend, Lacy Lynn White, was seriously hurt in the crash but survived).
Defense attorney Mark Fredrick acknowledged during his opening statement that Kirby had been drinking but placed responsibility for the accident on Lewis, saying he was hit after attempting to pass Kirby "at a speed that was absolutely frightful."
Lewis co-founded the Tapout line with friend Dan "Punkass" Caldwell in 1997. Known for an indefatigable work ethic and generous nature, Lewis helped make the brand a force in the world of mixed martial arts, raking in nearly $200 million in revenue in 2009. He was later posthumously inducted into the UFC Hall of Fame.
Kirby faces a maximum sentence of nearly 20 years in prison if convicted on all counts. The 53-year-old has two prior DUI convictions on his record, one in 1985 and another in 2002.