Doesn't really matter how you set up the approach if you fly through minimums without the rwy in sight.
In this occasion, They clearly wanted to use VNAV guidance to the MDA-and had they set it up properly (sequenced the FMS properly), the autopilot would have automatically disconnected while they were still IMC. Wishfully-that startling event might have prompted a go around and there wouldn't be a mishap to learn from.
They had mental image that they were excessively high. In reality, they leveled off 200' above the FAF altitude prior to the FAF-still kind of fast, but workable. IMO staying at 2500' was a conscious decision, something I do quite frequently on my VNAV approaches. That allows the automation to grab the intended descent angle prior to the FAF and allows a great altitude cross check crossing the FAF in the same way grabbing the ILS glideslope prior to the FAF does as well.
IMO-they also failed to cross check the stepdown fix. Had they caught how close they were to that altitude, quite possible the Capt would have backed the V/S off to the 700 ft/min he originally commanded after the automation failed to Capture the descent angle as he had expected prior to the FAF. (The Automation Didn't catch it because the FMS still thought they were going direct to KBHM, then back out to one of the initial fixes for the LOC 18 approach)
Then both of them missed the MDA. I think because both of them had an expectation that the Wx was better than it actually was. As the Acft passed 1000' MSL, sink rate warning was triggered, V/S was reduced, Rwy called in sight and the autopilot was disconnected-impact with the trees was 1 second later.
Of note: mins using the stepdown fix are 1200'; Airport elevation is 650' so typical stable approach criteria of 1000 ft/min started at 1650 and the 1500 ft/min descent was maintained well beyond that.
One of the great sayings I've heard in my career is "If I have to say what's going on when I'm on final I'm going around". One of the things I hated reading about in this CVR is how irritated the Capt was with ATC keeping them high for the approach-I promise you, if you tell ATC you want a 360 to better align for the approach or more time to setup for the approach, ATC will give it to you.
The WHY's of this mishap will be the subject of the NTSB meeting Sept 9th. Fatigue might or might not be one of the formal causes, but it's for sure going to be way up there.