The problem with these sorts of incidents is that, even if investigated and found to be baseless, the subject of that investigation effectively already has one strike against them.
If someone else decides to try and help the first complainant along by submitting a seemingly unrelated allegation, then the old "where there is smoke there is fire" system kicks in and the poor bastard is investigated again (rightly) but with a more jaundiced eye.
Everyone, regardless of their piety, professionalism and caution is guilty of some form of infraction of company guidelines, CASA rules or such - ever caught yourself at 61 in a 60 zone?
A creative investigator can build a damning case from very little if they want to.
The big problem that I see is that the perpetrators of these malicious and vexatious allegations are for the most part left unpunished. They should be dealt with the fullest extent of both the law and company policy, however as managers typically don't want to discourage the honest and legitimate report these scumbags are left with a slap on the wrist and a stern "don't do it again".
I can think of one bloke in a large carrier in Australia who made a number of false accusations about someone. That someone was investigated and found innocent of all the allegations yet his/her reputation was irreparably damaged and the accuser was unpunished. Given the outrageous nature of the allegations and the pre and post report behaviour of this individual, they should have been sacked, yet they continue on to this day.
The accused suffered significant embarrassment, stress, sleepless nights and humiliation, all at the hands of this tool and yet didn't even get a formal (or informal) apology from either the company or the accuser.