â€œAnd this also,â€ says Marlow in Conradâ€™s Heart of Darkness, â€œhas been one of the dark places of the Earth.â€ He was referring to England.

Those words are brought to mind by a pair of events: An important speech by FBI Director James Comey, and the bureauâ€™s admission, less than a week later, that its forensic analysts had been helping prosecutors railroad defendants.

Comeyâ€"at one time managing assistant U.S. attorney in Virginiaâ€"gave a speech at the Holocaust Museumâ€™s 2015 National Tribute Dinner, explaining why he makes every new agent visit that museum. In it he mentions that on a recent flight he had been rereading Holocaust survivor Viktor Frankâ€™s â€œManâ€™s Search for Meaningâ€(n.b.: not reading, but re-reading), and he has wondered how the Holocaust is â€œconsistent with the concept of a loving God.â€

Comey also finds two lessons in the Holocaust: mankindâ€™s inhumanityâ€"and, more troubling, its humanity. He wants his agents â€œto learn about the abuse of authority on a breathtaking scale,â€ but also â€œhumanity and what we are capable of. … Sick and evil leaders were joined by, and followed by, people who loved their families, took soup to a sick neighbor, went to church and gave to charity. Good people helped murder millions.â€

Comey served in the Justice Department during the George W. Bush administration. In probably his most famous moment, he refused to certify the legality of a domestic eavesdropping program. White House Chief of Staff Andrew Card and White House counsel Alberto Gonzales figured they could get it certified by Attorney General John Ashcroft, who was in a hospital intensive-care unit at the time. Comey raced them to the hospital and stopped them from prevailing upon Ashcroft. Then he and others threatened to resign unless the program were changed.

That act of courage and integrity earned him much acclaim, and rightfully so. Comeyâ€"a Republican who contributed to Mitt Romneyâ€™s presidential runâ€"also has signed an amicus brief supporting gay marriage. He has been raked over the coals by Sen. Jeff Sessions for daring to suggest the bureau might need to hire people with certain skill sets who also might smoke pot now and then.

During the Bush administration, he also spoke out against waterboarding, warning that future generations would judge it â€œsimply awfulâ€â€"although he did not, or could not, find a legal basis to declare the practice out of bounds. (During his confirmation hearings he declared it both torture and illegal.)

Less commendably, he has criticized Apple and other cellphone makers for including encryption technology that can keep even sophisticated snoopers in law enforcement from snooping on private communications.

He also has defended federal surveillance programs, as well as the indefinite detention without charge of American citizens and the FBIâ€™s use of national-security letters, which allow the bureau to demand all sorts of information from libraries, companies and others, with precious little justification or oversight.

No one is going to confuse Comey with Rand Paul. Then again, itâ€™s probably unrealistic to expect any director of the FBI to epitomize the Platonic ideal of a civil libertarian.

Still, Comeyâ€"who keeps on his desk the order from J. Edgard Hoover and Robert F. Kennedy to wiretap Martin Luther King, Jr. as a reminder of how the bureau can go astrayâ€"seems more keenly attuned to the danger of concentrated power than most people in such powerful roles.

As he said in his speech about the Holocaust Museum: â€œI want (our agents) to … realize our capacity for rationalization and moral surrender. I want them to walk out of that great museum treasuring the constraint and oversight of divided government, the restriction of the rule of law, the binding of a free and vibrant press. I want them to understand that all of this is necessary as a check on us because of the way we are.â€

That sensitivity will be needed as the FBI moves forward with an investigation into what could be one of the most damaging foul-ups in its history.

The FBI has now admitted that nearly every forensic examiner in a unit dedicated to microscopic hair analysis provided flawed testimony in hundreds of cases. And 95 percent of the time, they did so in a manner helpful to the prosecution.

This isnâ€™t some minor technical detail without real-world consequences. In the District of Columbia, defendants and prosecutors have reviewed several convictions that relied on FBI hair analysis. In five out of seven cases, men convicted in rape or murder trials where the FBI gave flawed testimony have been exonerated by DNA or the courts. Five out of seven.

Around the nation, roughly 1,200 similar cases remain to be examined. Even if the ratio in those cases is far smaller, one unit in one department in one branch of the FBI could have sent scoresâ€"perhaps hundredsâ€"of innocent people to prison for decades. Not by accident, but by repeatedly overstating their findings to help prosecutors.

The analysts responsible for that were not among historyâ€™s greatest monsters. They were not tyrants maniacally determined to exterminate an entire race. Not even close. They were people who loved their families, took soup to a sick neighbor, went to church and gave to charity.

And yet.

Comey doesnâ€™t have to send new agents to the Holocaust museum to learn that good people can abuse power. To learn that, they donâ€™t even have to leave the building.