how can I find deleted files on facebook group. if I just as member of that group.?

[Geni]

I followed an investment group as a member in facebook group. Admin of the group collects money from members of the group for the purpose of investment. And each investment period, the admin made a list of names and the amount of money in the right investment. But the original investment which good looks, turns problematic and admin of that group was guessed cheating or helped other man to frauds occurred.
To get rid of the evidence, files in the group is then removed by admin How can I (that my status as a member of the group) can get the archive one or several files which deleted by admin, as evidence?
thank you

[pri✍]

Deleted is deleted, gone, no way to retrieve it. You should make screenshots of it before it's deleted.