-IMHO even a tiny minority of actual, true, false positives are enough to warrant getting rid of capital punishment (for that reason alone; there are other arguments, too!)
To phrase my question differently - if we take your concerns about false positives into account, and accept that trying to help dispose of the body or providing a weapon makes you fair game, capital punishment-wise - how large a remaining false positive rate is acceptable to maintain that fine institution, capital punishment?
1 in 100 fine, upstanding citizens being wrongfully convicted and executed? 1 in 1,000? At which point is the collateral damage, if you like, acceptable?
The matter was discussed here on HN recently, in the case of Kevin Cooper[0].
That's but one instance of what seems like a case where there's definitely reasonable doubt - to put it mildly - regarding the convict's guilt.
Whether the person was a 'fine, upstanding citizen' IMHO is largely irrelevant, unless one wants to set the bar for being sentenced to death lower - like, for being an accessory to murder, for instance.
[0] https://news.ycombinator.com/item?id=17098059