After contradictory stories emerged about an F.B.I. agent's killing last month of a Chechen man in Orlando, Fla., who was being questioned over ties to the Boston Marathon bombing suspects, the bureau reassured the public that it would clear up the murky episode. But if such internal investigations are time-tested, their outcomes are also predictable: from 1993 to early 2011, F.B.I. agents fatally shot about 70 subjects" and wounded about 80 others - and every one of those episodes was deemed justified, according to interviews and internal F.B.I. records. The last two years have followed the same pattern: an F.B.I. spokesman said that since 2011, there had been no findings of improper intentional shootings. In most of the shootings, the F.B.I.'s internal investigation was the only official inquiry. In the Orlando case, for example, there have been conflicting accounts about basic facts like whether the Chechen man, Ibragim Todashev, attacked an agent with a knife, was unarmed or was brandishing a metal pole. But Orlando homicide detectives are not independently investigating what happened. Occasionally, the F.B.I. does discipline an agent. A typical punishment involved adding letters of censure to agents' files. Critics say the fact that for at least two decades no agent has been disciplined for any instance of deliberately shooting someone raises questions about the credibility of the bureau's internal investigations.