I have never heard of, and I can't imagine how, a carjacking would result in the passenger window being broken. The gas station attendant in Troutdale who saw Whitney and the driver acting suspiciously at 9:14 AM made no mention of Whitney's window being down/missing/broken even though the temperature would have been in the 50's. I'm wondering if the broken window came latter. Perhaps something went wrong such as the perp locking the keys in or Whitney locking the perp out.
The gas station where she was seen at 9:17 is only about 2 miles from both Whitney's Apt or her place of employment yet this was over 2 hours after the probable abduction. My guess is the perp did what he was going to do during that time frame. But why return to the scene of the crime (the abduction).
One possibility is that he did what he did somewhere in the Gresham area but this plan was then to take Whitney out of town and the car was low on gas. If he was done with her and planned to kill her, why was she still alive? Traveling with an abducted girl would be very risky. Perhaps he wasn't done with her. Also, in Oregon, a gas station is a good way to "test" a debit/credit card since you can use it without leaving the vehicle. Perhaps he wanted to be sure it worked and the PIN she gave him was correct. (He may have wanted her alive until he was sure the card would work) We do know he used the card "several times" but we don't know where or when and we don't know if it worked.
One could drive to the Larch Mountain area and return easily in 2 hours. He could have gone there between 7:00 and 9:17 or he could have gone there between 9:17 and soon after 11:00 AM, when the vehicle is believed to have been dropped off at Walmart. He could have gone to the same place twice, but he would not have needed to return to that gas station. (there are plenty of gas stations along Hwy 84)_My guess is that the Perp either changed his plans or was working "on the fly". He sounds like he was not so well "organized".
One possibility is that at some point after the gas station he left the vehicle at an ATM and Whitney was unable to escape but she was able to lock all doors. The Perp may have had to break the glass. He may have panicked and changed his plans at that point.
The Wal-Mart where the vehicle was dropped was about 2-2.5 miles from the probable abduction site. He would likely either live near there or have his own vehicle stashed. I hope video cams along probable routes south are being checked.
I'm willing to bet he either lived near her, knew her for that reason and abducted her from the Apt parking area or he knew her from Starbucks and abducted her from the area where she parked (most likely the former).