Yes, it's legit

"To be blunt Mr. Holder, I am appalled at your lack of leadership as the Attorney General of the United States and your blatant politicizing of the Department of Justice. Your actions, both publicly and privately, have done nothing to quell the complex racial issues we face in our country and have done everything to inflame them. As the "top cop" of the United States, you share in the blame for much of the violence and protests we are now witnessing against law enforcement officers honorably serving throughout our nation." - K. Dee McCown, Former FBI Special Agent (1997-2008)

For the Lefties who diss these letters that show up in blogs or other social meda, even Snopes has verified authenticity on this one.