I still can't decide if Mueller knew all along that Manafort was a double agent and played along to trap them or if Manafort got away with it for a little while. I believe it was the former but who knows
"Never ask a question that you don't know the answer to"
How not to conduct a cross examination is illustrated by this classic (and supposedly true) story from a trial:
A man was being prosecuted for criminal assault for biting off the ear of another man during a fight in a bar, and a witness had taken the stand and testified that the defendant had bitten off the ear of the other man. The defendant's lawyer proceeded to cross-examine:
Q: The bar was quite crowded that night, wasn't it?
A: Yes.
Q: And the two men who were fighting were rolling around on the floor, were they not?
A: They were.
Q: And while they were rolling about, one man would be on top, and then other, correct?
A: That's correct.
Q: And there was pushing and shoving and shouting around you by other people watching the fight, isn't that right?
A: That's right.
Q: So you couldn't see the fighters all of the time, could you?
A: That's also right.
Q: In fact, isn't it true that your view was so obstructed that you didn't actually see the defendant bite the ear of the other man?
A: Yeah, you're right. I didn't really see him bite the ear off.
At this point, the lawyer should have quit. But something in him made him ask one more question.
Q: So why did you testify that the defendant bit the ear off?
A: Because I saw him spit it out.
It is difficult, in my mind, that Mueller and his team would trust Manafort to any degree particularly after he was jailed earlier for attempted witness tampering. Mueller was more likely letting his bait swim around expecting to hook a much larger fish!