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This is just a little funny theory I was reading, but a plot hole in BttF makes Doc Brown a murderer.

In BttF 2, it is shown that when you travel in time through an alternate timeline you do NOT replace that timeline's version of yourself, as we learn that there is currently a version of Marty in a boarding school and Emit Brown is in a mental hospital. We have to accept this as the rules of the franchise.

This brings us back to BttF1. At the end Marty witnesses himself go back in time to 1955. However, this is no longer the same Marty, as it is an alternate timeline. This means the alternate timeline Doc Brown, knowing Marty would be born, inserted himself into Marty's life, and set up this scene to match what he saw in original Marty's video. But what happened to the alternate version of Marty? If he went into the past he himself would alter the timeline. Doc Brown needed to send him somewhere he could never alter the lives of people in 1985, and that means far into the future, never to return.

The film would suggest that there is only one timeline with rather loose rules of causality applied to anyone travelling through time.

If there were multiple timelines then Marty would have been unaffected by the changes to his own past, because they would have been a different Martys past.

Uh, it's a completely standard time travel loop?

If we do accept this version of events, you've not explained how Doc kills any version of Marty.