What she said
After Yoon was released from jail, he and his wife Kim Keun-hee had a big fight. According to someone close to her, Kim said:
계획해 놓은 것이 많은데 왜 계엄을 했느냐? 너 때문에 망쳤다
I'm going to translate this in the passive tense - because the statment does not indicate personal culpability:
So much planning was done, why did you have to declare martial law? You ruined everthing."
The special prosecutors are interpreting this statement to argue that this meant that she was not involved - but that argument seems a bit dubious. The fight was after he was released from jail, and months after the declaration of martial law.
If anything, the statement suggests that Kim was more angry about the timing of the martial law declaration, rather than an admission that she was not involved. This also fits into the conventional wisdom about the insurrection. In part it was meticulously planned. But Yoon put it into action impulsively, haphazardly, when the people responsible for pulling this off (especially the army) were not ready.