I see the learjet performed 12 flights before the accident and no one said anything.
12 flights in 2012 that were recorded by Eurocontrol. There could have been others (local VFR or VFR between small airfields like his homebase)!
But who should have said something, and on what basis? I fly bizjets too, but I know almost nothing about the types that I don't fly myself. There are quite a few single-pilot jets around, how would I know, if this type of Learjet requires two pilots? And why would I care, am I a policeman or what?
And regarding his fake license(s): As he flew to some larger airports with security gates too (LFSB, LEPA, LOWS, ESMS), I'm almost sure that he had to show his license and documents more than once. If they were good enough to fool security personnel and border police, why should anybody else become suspicious?