The court documents on that case are publicly available if you're willing to look for them (and can read Russian). I haven't read everything, but I didn't see anything contradicting his side of the story.
he said he was "driving home at 3am," you know, as one does, and two girls were "crawling on the highway." i am honestly not sure i've ever heard a less believable story
I have been driving home after midnight, coming from my where my parents live, a long distance away, and encountered a man who had climbed up into the elevated highway. It was straight and well-lit, but the best I could make out was that he was running at cars wielding a cardboard box (?). I began to decelerate and moved into the lane furthest from him, at the time, and after another car in front of me passed him, he moved into my lane. I'm still braking to slow down, and I change lanes to avoid him again, swerving and praying the lights in my rear view are slowing too and don't hit me as I try to avoid this man.
As I pass him, I manage to be one lane to his left, and he makes a lunge to try and jump in front of my vehicle. With some frequency, to this day I wonder how fucked I would have been if he succeeded in jumping in front of my car. The story I tell myself is that he was mentally unwell and thought he was heroically "tilting at windmills". It is more likely he was belligerently drunk, or was suicidal and wanted some help in it.
I don't know what makes something believable or unbelievable in your mind, but these are the details of an almost-incident that happened to me.
I have a friend who went through almost exactly the same driving event as this guy. Hit a man wearing all black on a country road at 1AM. Could have driven away but called 911, rendered first aid, and stayed through the ordeal. He also ended up spending several years in US prison for it.
Russia does not have a "justice system" in the way that we would understand it in the West. Instead it has (and indeed, always had) a system of patronage and bribery, where your status within the system determines your sentence. If you are an oligarch, or the son of an oligarch, you will walk free, unless you cross Putin. If you are a nobody, you pay off the right people or you go to prison or end up freezing to death in a foxhole in the Donbass (Wagner recruits directly from prison, just as Stalin emptied the gulags for his cannon-fodder in WWII).
That's just how Russia is and always has been, and unfortunately, very likely always will be.
Is Denis guilty? Perhaps, but he will not have had a fair trial by any Western standard, and so we have to presume innocence.