 Complete the following phrase:  Despite the severity of his wounds, Dobyns refused disability retirement and returned to duty within months of the shooting. For the next two decades, he conducted over 500 undercover operations, developing expertise in violent crime investigations, weapons and narcotics trafficking, gang infiltrations, home invasion burglary and murder-for-hire cases. He also served as an instructor at ATFs National Academy and member of the Bureaus Enhanced Undercover Program. He was repeatedly detailed to high-profile criminal and terrorism events including the Rodney King riots in Los Angeles, California, the 