"Based upon the unique circumstances, the public interest requires me to place this investigation under the authority of a person who exercises a degree of independence from the normal chain of command," Rosenstein said in a statement. "A special counsel is necessary in order for the American people to have full confidence in the outcome. Our nation is grounded on the rule of law, and the Public must be assured that government officials administer the law fairly."
UPDATE - President Trump issued this statement regarding the appointment of Robert Mueller as Special Counsel:
“As I have stated many times, a through investigation will confirm what we already know — that there was no collusion between my campaign and any foreign entity. I look forward to this matter concluding quickly. In the meantime, I will never stop fighting for the people and the issues that matter most to the future of our country.”