I've had my suspicions since not long after...your mother's death. I did some under the table digging to find out what her Shadow meant, and found out she was a former associate of Shido's, who stopped working near him after she became pregnant. We also share an incredibly rare blood type.

[He pauses, then holds the bag of fudge cookies out in front of her. She...looks like she could use some comfort food.]

I wasn't sure until I talked to Shido in the forest. He confirmed my theory as to why he'd gone to so much effort to pin the blame for her death on you, when it would have been far easier to simply pass it off as a known workaholic passing out from exhaustion.