Staying out of the discussion and focusing purely on the aviation aspect:
Aviation safety network link:
https://asn.flightsafety.org/wikibase/484185
This "ADS-B data indicates the aircraft was cruising at 9675 ft baro when it approached an area with several mountain tops and began a descending right hand turn which progressed into a spiral. The last ADS-B return showed an average rate of -17250 fpm. "
indicates the classical graveyard spiral of a non-IFR rated pilot flying into IMC (the cloud).
"At 0930 LT, about 10 minutes after the accident, the nearby Ljubljana Airport automated surface observing system reported winds from 320 degrees at 7 knots, ~4.5 miles surface visibility, light rain, 2000 ft above ground level (agl) broken layer and 3200 ft above ground level (agl) overcast ceiling, temperature 9°C, dew point 8°C, and an altimeter setting of 29.74 inches of mercury. "
indicates that icing was likely not a factor.
Looks like he managed to buy a very nice aircraft off his ill-gotten gains, the 2005 M20R is a sweet machine, but no turbo-charged engine to stay above the clouds (though at some point you have to come down). Maybe too much aircraft to handle, it's fast as, easy to fall behind the thing.