If he spent the 26th to 28th with AK and went to work on the 29th, where was AK on the 29th? Did he drive her to work that morning (as he says he drove her to work the morning of the 30th, prior to finding AG's body).
NSU, your cupcake brings us back to THE CAKE !!! Did he get out of his car, expecting to meet and greet AG cake in hand, open the garage door, find AG's body, dial 911, go back to check for a pulse, return to the car ... what was the cake doing during all this? Was it found placed delicately in the garage? Was it sitting in the car waiting? Waiting for what? If it existed, it should have been in his hands because he would have had no reason to NOT have it with him if he expected AG to be alive and well.
Other than spouses corroborating each others account, who else can corroborate that PK and AK were together at all times from the 26th to 28th? Most young couples with familys would be out and about, visiting with family and friends during the holiday season.