Subaru Outback won't turn over

I recently purchased a 2001 Subaru Outback 2.5 Liter with 76000 miles. It is from out of state and I wasn't able to personally test drive it. A friend test drove it for me. While test driving he shut the vehicle off and then was unable to get it to even turn over. The passenger was a mechanic and thought to tap the gear shift and it started and ran fine. (We think it might be a neutral stop/safety switch). On the way home from the destination the vehicle killed at a stop light and several minutes later after jiggling and jostling everthing in the vehicle it started. It then drove fine the remainder of the distance to his house roughly 3 hours on interstate. I had sceduled to have another friend finish the relay to my home. The next morning he was in route to the rondevous point when he pulled over to run an errand and found the car again dead. Frustrated for both him and myself I called a tow truck. When the tow truck eventually got there 1 1/2 hours later the vehicle started without problem and he drove it up on his trailer. I have no idea what is causing this because I now have it at my home and have driven it and shut it off and restarted it with no problems. I am afraid it is going to let me down sometime when I need it most. Any idea what may be going on?? Any help will be greatly appreciated.

Thanks,
Ben