It would keep your testimony from being thrown out. A memory will back your words. The prosecution will be doing their level best to throw out anything they can. Always keep in mind that evidence used needs to have impact that sways opinions in our favor.

Any cross-exam is done with the lawyer or detective, or questioner trying to control you. They will ask things with a goal in mind. Or to discredit you.

[He could get the memory where she admitted killing her sister, but how much relevance does that have? He'll discuss it with Kirigiri.]

Anyway, the members of the first killing life Enoshima established, were her own classmates.