We don't. It's one of those secrets LE holds from the public.
There were accusations on here that noted that DR lifted the tape in the morning and drove over the print field. Is this substantiated? And if so, can someone post the source? What time of day is Steve Mund creating the casts?
Follow me on this strictly hypothetical scenario.
Two perps scouting St Joseph for kids drive past the boys while they were on their way to the store. Knowing that they would have to return that way, they begin to scout for a place to hide. They find DR's driveway and drive up and around the turnaround near the house. DR sees two people in the cab, a driver and either a child or woman. They park the car a couple hundred feet shy of 91 as to not be detected by other passing potential motorists. On the way back the kids are easy to spot with their fluttering flashlight. One of the perps walks down to the end of the driveway beginning the abduction. Jacob is selected and walked back to the car and placed in the trunk (notice the foot cast on top of track in Shergals image). The abductors drive down the remaining part of the driveway with their lights off. Once securely on 91 they turn their lights back on. Both Trevor and Aaron would have been in a mad sprint towards home, most likely not turning around to see if there were any vehicles exiting the crime scene.
In this scenario the two parties DR saw in the car are explained. Also, anyone who's ever spent a long time in the dark knows that their eyes begin to adjust. It wouldn't be hard at all to guide a car a couple hundred feet down a straight driveway with the lights off. That would account for the boys not seeing any lights directly after the abduction.
The only loopholes in this scenario are the tire tracks that LE says are now all accounted for. However, I think it's been WELL established that the Stearns County Police Department has made substantial errors in the past. So my scenario is adjusted and catered towards this being the case. Curious to see what your responses are.