Is it possible to remove/delete/modify the attachment from a Supplier negotiation response?

Summary:

Our customer currently has a claim from a supplier where the supplier says that he created a response for a negotiation including an attachment. The supplier was disqualified on that negotiation because the response didn't have any attachments on it.

Now the supplier is saying that someone removed the attachment from the response. (We need to certify this is not actually possible).

Content (please ensure you mask any confidential information):

We need confirmation from Product/Support detailing if this is possible (To modify/delete the attachment from a negotiation response) (As negotiation team member or employee). Also if this is not possible, is there a certification from Oracle where it explains that no one can remove/delete/modify the attachment from a negotiation response?.