So, this came up in a Facebook thread a while ago, figured I should put my theory here.
So, we should all know that at the end of Back To The Future, the Libyan terrorists that Doc Brown got the plutonium from shot Doc Brown at point blank range with assault rifles, and Marty returns from his near incestous diversion to 1955 to find the terrorists crashing into a photo booth, and Doc Brown getting up barely even winded.
There are issues here. Plutonium, from terrorists? Uranium, maybe, you can mine that shit. But plutonium needs to be produced in a nuclear reactor, and is typically monitored very closely by national and international watchdog agencies. There’s a country short on plutonium that has likely deployed their entire intelligence service to find it. Intelligence services of other nations probably got involved the instant the IAEA was notified.
And odds are, those Libyans aren’t the only people in their org that know about the plutonium. Their next senior commander is going to want it found as well, as well as wanting to find out what happened to their men. And, oh, the odds the crash was fatal appear to be low. I’ve been in much more severe car crashes and walked away. With that many people and at least one unbelted, there were likely injuries, but they would have survived. One of them might have even got away before police arrived and immediately called in the CIA. Seriously, there’s just no way Doc and Marty are getting away from the police.
Doc and Marty would have been immediately picked up. Marty was probably released fairly quickly, maybe the feds cut him a break as a stupid kid, maybe Doc Brown secured Marty’s release as a condition of cooperating with DARPA on developing new technology. Hell, Doc’s bulletproof vest alone would be worth billions. Point blank fire from multiple assault rifles on full auto and all that happens is you are knocked on your ass? With minimal movement restriction on an old man probably not in the greatest shape? This would be one of the most fundamental advances in infantry combat since the machine gun. A trained soldier in good shape could probably have killed all of those terrorists with little trouble. This vest is close to being as implausible as the time machine itself!
At some point Doc Brown manages to access the confiscated DeLorean(perhaps his minders let their guard down while he was consulting on its analysis?) and escapes to 2015, setting up the second movie. But Marty? After the feds let him go, the Libyans catch him. Perhaps one of the terrorists got away, perhaps other cells managed to track him down while looking for the uranium. He’s put through hell to get him to talk. Given that he was living openly in 2015, I suspect that at some point prior to his release he managed to convince the terrorists that he didn’t know anything, and they got that information transmitted up their chain of command. Then the cell he was held by was probably wiped out by SEALs or something, so they weren’t worried that Marty could give the CIA useful information on them.
1985 Marty was a reasonably well put together teenager. Not hugely special perfect teenager, but nothing extraordinarily horrible. 2015 Marty? He was a bit of a wreck. Nervous, even more afraid of being called a coward than he ever was in 1985. Why? Psychological trauma resulting from torture at the hands of Libyan terrorists, and possibly even some from the CIA.