The elevation and photo of the crash site is interesting and I think casts some doubt on whether this was a simple case of a VFR flight with loss of control following inadvertent IMC entry in poor weather.
The impact location at a ? reported 2300ft is only just below the peaks in the area and much (? circa 1500 ft) higher than the valley that the aircraft presumably flew over a few miles before it crashed. If this aircraft was VFR, it is hard to see why the pilot would not have followed this low valley, south to Dolgellau and then west to the coast at Barmouth - the cloud base and visibility was likely to have been far better. Again, assuming he was VFR, he had somehow got himself to south of Trawsfynydd and given the equally hilly terrain to the east that he had passed, the weather had not been so bad that he had not been able to get himself this far.
To hit the mountain where he did, if he was VFR, it would seem most likely that the cloudbase was far higher here than many have presumed, perhaps around 2000ft. The pilot could well have thought that he just had to clear this mountain peak and then 3 miles later he could descend rapidly towards the coast at Llanbedr. With this scenario, he can't quite make it, climbs into IMC, loses control and crashes. But if the weather was this good, why would he had not just have chosen an easy cruise down the valley to the coast?
The view that seems to generally assumed to be the case by most posters here is that this pilot was groping along trying to maintain VMC, which would have meant a much lower cloudbase - elevation was down to less than 400ft in the valley that he had just crossed, so if his height was say 300ft that might have meant a cloudbase of 700ft AMSL. The idea that the pilot got into IMC inadvertently and lost control of the aircraft, yet managed to climb over 1000ft before crashing is unlikely I think - with this heavy, low powered aircraft, that would have taken a couple of minutes of solid controlled climbing and I'm sure most of these IMC LOC accidents occur within seconds not minutes.
I feel that a more likely possibility is that this pilot was deliberately flying IMC - and hit the mountain top. It seems likely that this AS355 was IFR equipped, or IFR of sorts, and putting to one side whether the pilot had an IR or not, he may well have been comfortable flying IMC, engaging the autopilot and flying in IMC. Indeed a previous poster mentioned he was at 2700ft earlier in the flight - if correct, given the weather, he would probably have been IMC then.
So if he was IMC, why might he have hit the mountain top? Clearly he may have had a mechanical failure, though this is statistically least likely. Another possibility is that he encountered icing and either descended too quickly in panic, or simply could not maintain altitude with ice on a heavy 355. Or may anti-icing was not on and an engine or two flamed out - Alton Towers memories. Then he could have had a gyro or autopilot problem which was not noticed. Or instead of having ALT engaged, had VS and that was actually in slight down so caused an unrecognised gradual descent. And finally of course he could mis-read the chart and descended a bit too soon for the coast and to get VMC.
So in summary I think there is a lot more to consider before people start making assumptions about the cause of this accident and what should happen as a result. Something that happens too much following aircraft accidents is that a lot of generalisations are made and not enough focus on actually understanding what specifically caused the accident.