Without that keyring, no, I don't believe there is definitive proof. But according to the aunt, Chandra was in his apartment without Condit frequently, making dinner before he was back from a session, etc. The aunt told of one phone conversation she had with Chandra from the Condit apartment, Chandra was bored and the aunt suggested she rearrange his closet. It would not have been possible for Chandra to get into his apartment without him if she did not have a key to the front door -- unless Condit was in the habit of always leaving the door unlocked.