Washington (CNN) Christine Blasey Ford's sister-in-law said Sens. Joe Manchin and Susan Collins were trying to have it both ways when the senators said they believed Ford was sexually assaulted but not by Supreme Court nominee Brett Kavanaugh.

Ford has accused Kavanaugh of sexually and physically assaulting her more than 30 years ago while they were both at a party during their high school years. Kavanaugh has denied the accusation.

Manchin, a West Virginia Democrat, and Collins, a Republican from Maine, said they believed Ford when she said she had been sexually assaulted but that they didn't think there was corroboration to prove it was Kavanaugh.

"I think it's their way to sort of get out of this difficult bind that she is believable and that this type of behavior is completely unacceptable. There would be no way to make it acceptable. So I think they are diverting away from the main issue and trying to create an alternative reality, really," Deborah Peters said on CNN's "Erin Burnett OutFront."

The FBI conducted a supplemental background investigation into the allegations against Kavanaugh, and members of Congress were able to see the results of the probe starting Thursday morning.

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