Bruce Beresford-Redman's wife, Monica, was found dead at a resort in Cancun last year.
Witnesses said Bruce Beresford-Redman tried to hit his wife, and the two argued in their room.
But on Monday, his lawyers filed a sworn declaration by a therapist who said the couple's young daughter did not see her father hit her mother and that they didn't argue.
The family of Monica Beresford-Redman said in a statement that they were "stunned and saddened" by Bruce Beresford-Redman's latest move.
"We are shocked at his shameless use of our young niece as his alibi when all of the available evidence points toward his guilt. We hope and pray that such abhorrent tactics will not prevent justice from being served in this case," the family said in a statement.
Beresford-Redman is in federal custody, awaiting possible extradition to Mexico. An extradition hearing is scheduled for next month.