From the AMA:
Q: Is there evidence he actually drove himself there / etc.
Yes. In addition to UPS Store cameras (which is how we know he changed clothes in his car afterwards), his car's journey was tracked via various FastTrak and traffic cameras from leaving that store (where he dropped off a return item) until getting to the trailhead. He'd also called his wife that morning before setting out with his rough plan, and texted her from the trailhead to give her his ETA.
Chris Thoburn 7/23 AMA Q&A Responses
The only way they would know he changed clothes in the car based on UPS footage is if he was seen in UPS in regular clothes and not running clothes. I personally find it odd that he didn't leave the house in his running clothes.
Reportedly the shirt he was wearing in the photos from Friday evening, it is also on the missing poster. I also found that strange, he drives a hybrid sedan so not much room to change, lots of odd details.
Does anyone know what clothes were found in the car?