(FOX 2) - Former Detroit FBI chief Andy Arena calls Robert Mueller one of the best bosses he ever had.
He says Mueller was so tough he probably wouldn't want to work for him again but the adjective Arena uses the most to describe Mueller is "fair."
"When this started, everybody was behind Bob Mueller and then the Republicans said they were against him and the Democrats were supporting him and now as you see today, it has basically flipped," Arena said. "One of my mentors early in my career with the FBI told me, if everybody is mad at you, you probably did the right thing.
"Bob Mueller doesn't care what other people think of him, he is going to be thorough and he is going to do the best job he can."
Arena knows tough plenty about tough, high-profile cases. The federal investigation of Detroit Mayor Kwame Kilpatrick hit its stride while Arena was the special agent in charge of the Detroit Office of the FBI.
Now that Mueller has ruled out collusion, he is facing criticism for declining to say whether the president interfered in the investigation. Arena says that's a tough call to make.
"When you're talking about obstruction of justice and perjury, those are some of the toughest, most difficult cases to ever make," Arena said. "Because you may have evidence but you may not have intent."
Mueller's investigation has prompted federal prosecutors in New York and Virginia to bring charges against multiple Trump associates.
Arena suspects the full Mueller report - when it's released - may just fuel more speculation about the president's inner circle.
"There's going to be a treasure trove of information in that report," Arena said. "When you start kicking over rocks, you don't know what you are going to find. The Mueller investigation is a great example of that."
FOX 2: "It sounds like you are saying this is not the end, it is just a new beginning?"
"Your political leanings are going to cloud your optics as to how you look at this thing," Arena said. "It depends on your political view."