In your example, there is no reasonable doubt that the accused was "driving a red pickup truck with a damaged right tail-light", right? And there's no reasonable doubt that a video exists of him drinking with the deceased earlier in the evening, right (although I'm not sure how that's relevant unless he claimed to not know the victim at all, or he had an alibi that was contradicted by the video)?
In my scenario, yes. But it is not required. At some point you have to arrest the accused. Let's call him "Dave". There could have be a friend who said he saw his friend Dave (whom he knew) driving his red pickup truck and noticed that the truck had a damaged right tail light. You could question whether he was correct. And there could be doubt that the video shows "Dave" with the accused - it could be poor resolution and just show a guy with a beard who could be Dave. It doesn't matter if you have enough pieces of independent evidence.
If there is reasonable doubt of these things, then it's a whole different conversation.
Not at all. First of all, it is a mistake to apply reasonable doubt to a piece of evidence. Say you have a picture of Dave killing the victim. Would you say "oh, it is just a digital picture and show the jury one pixel at a time and ask: does this look like Dave?". The jury would say, "no it doesn't but when you put them all together I see Dave killing the victim". That is an extreme example but it is kind of how evidence works.
Instead, let's say for example that the cops claimed he was arrested "driving a red pickup truck with a damaged right tail-light", but they lost the truck, or they produce a photo of the truck but it doesn't have a broken tail-light. Or there are witnesses to the arrest who say he was arrested in a blue car...
It all depends on what the other evidence shows. But these things really don't happen that way. When someone drives away in a red truck, two minutes later they are likely still in the red truck. If a person is stopped in the blue truck, they are probably not going to fit the description because they are not the culprit. You can make up anything you want and say "what if a guy fitting the exact description is stopped but he is in a blue truck" but that is very unlikely to actually occur.