The IG can’t prosecute or even reprimand anyone.
"Horowitz wrote that he will explore “allegations that Department or FBI policies or procedures were not followed” in connection with both [Comey] letters. When he is finished, his office will probably issue a lengthy report detailing what it has found, as it has done in other high-profile matters, though it is also possible he could recommend criminal charges for anyone found to have broken the law."
But he can produce evidence leading to all that.