The problem as I see it - the only person with new keys was the party complaining the property was stolen. The party complaining is not able to prove the ex took the items. The party complaining may very well have given the key to a friend to go pick up the property and is now just starting trouble for the ex. The party complaining cannot prove that they never received the property. The party complaining should have called the police and filed a report. That the home was not broken into would have been noted. That a TV was in the house but was not the TV for which the complaining party should have had a receipt would have been noted. If the complaining party had the right from the landlord to change the locks, then presumably they were a party to the lease and therefore would have been included on the renters insurance and should have been able to make a claim against the insurance.
The party complaining then would be walking into court with their receipt for the TV, their police report of a missing item from a location that showed no evidence of a break-in and where the "robber" kindly replaced the TV with another one and a denied insurance claim. But they didn't do that due to their belief that theft is a civil matter.
So basically, the party complaining is walking into court with a "he said/she said" situation. If you're lucky your case will be heard later in the day when the judge is tired and is fed up with all of the ridiculous shennanigans people do to spite one another. Other than that, frankly I think you're out of luck.