It may be difficult to weigh this against your original question regarding deliberate (and therefore malicious) prosecution of a person known to be innocent. However, there are some situations were a decision is made that 'the ends justify the means'. I recently used the term 'patsy' as you are aware. I suspect that there are some situations where the lines become blurred, between the security services, military and the police. Not overtly or publicly, but 'in the interests of the state' and behind the scenes. How much is known by the police officers involved in these scenarios is debatable. However, I would expect it to make sense that information was on a strictly need to know basis. Following this line of thought, I would expect that only some senior police officers would know for certain, that the person being pursued was innocent.
Where there is a political dimension to a case, I think you are right that they will not stick to strict investigative goals. Politics can come into it a lot, even with seemingly mundane criminal cases like the McCanns.
However, I'm not sure I can accept that they go round framing innocent ordinary Joe Bloggs type people. There is a fine line, but when it goes wrong, it seems to me it's more about either a mistake in the investigation, or officers have got a bee in their bonnet about somebody and they break the rules to get them convicted or the evidence has been misinterpreted.
In all cases, they think, believe or assume - or 'know' - that the individual is guilty or caught up in it in some way, and that's what drives it.
It's a
consequentialist attitude to ethics.
Take somebody like Dick Holland. It's not that he thinks an individual is innocent, though that may have happened with career criminals he wanted to set up in order to bang them up - which is a good example of consequentialist ethics in itself.
With regular people like Kiszko, the mindset of detectives like Dick Holland is more along the lines of:
Kiszko did it.
Oh, wait, we've got some evidence that might make a jury decide there's reasonable doubt.
But Kiszko did it and we need him locked up.
Hide the evidence from the trial so that we can get the result we want.
Job done.
It then turns out that Kiszko didn't do it.
Whether it's stupidity or malice on the part of the police officers, I'm not sure you can say they believed Kiszko to be innocent. Certainly, it's perverting the course of justice.