An indictment is not an arrest. An indictment comes from a district attorney while an arrest comes from police. The two don't even have to be associated with each other as a person can be indicted before they are arrested, or vise versa.

An indictment is a motion to proceed to trial, and often doesn't even require the availability or presence of the person. An arrest is a detention of a person to police custody.

The point: there aren't gonna be criminal consequences for a bad cop who made a wrongful arrest if it never goes to trial.

QI shields them from civil suits, so they're quite well protected on both fronts.

Even more to the point is that there is a readily identifiable problem. It is better to put energy towards fixing the problem than apply a really shit work around with horrible second and third order sequences only for the point of doing what you couldn't do the correct way.