Public corruption hearings are an anomaly because criminal investigations are generally conducted in private, to protect witnesses from physical or reputational harm. Criminal charges and evidence go public only when the case goes to trial.
There is an important difference, however, between police investigations and investigations by a corruption watchdog, an anti-corruption commission.
Consider that victims of ‘private’ crime usually know a lot about the crimes committed against them. Thus, a mugging victim might know all there is to know about their mugging; and retains that private knowledge regardless of whether the case proceeds to a public trial. From the perspective of the mugging victim, the work of the police is reduced to verifying the victim’s story and filling gaps in a story that the victim privately knows to be true. In contrast, watchdogs investigate crimes against an unknowing victim, the general public. Members of the public should also know what has been done to them but have no direct experience of ‘public’ crimes. For that reason, and subject to considerations of witness protection, watchdogs should have the option of inviting the general public into the interview room. The more serious the allegation, the greater the need for public understanding of the crimes committed against them.
Possibly, we should think of corruption hearings as akin to coroners’ hearings, which are routinely held in public. The victims are dead, have died in a violent or suspicious manner, along with their private knowledge of what happened to them. The public has no direct experience of the crime or misadventure but these are serious matters that the public needs to understand, regardless of whether anybody then goes to a public trial.