But wouldn't it be prudent to not kill potentially innocent people? God can sort out the wrongful life sentence given to an innocent person by a fallible judicial system.
Using your logic, in times of war we should just use nuclear weapons to obliterate the enemies infrastructure even at the expense of killing innocent civilians. "Let God sort them out."
Why are people only able to see the sacredness of the unborn but not of the living?
Evidence. Usually it all comes down to evidence. People get set up, framed, and yes, sometimes the set up is discovered and the innocent accused exonerated. Other times the innocent one ends up in jail and eventually death row, simply because the evidence was manipulated to show that they did it. In a court of law, sometimes all you need is circumstantial evidence.
For example, say "John" had a physical fight with "Jane" and several people witnessed this. Then a few hours later, "Jane" is found dead in her house. What NOBODY knows, is that while John and Jane were out on the sidewalk fighting, someone was in Jane's house waiting for her, and kills her when she comes in from fighting with John. Let's say the intruder is her ex-husband "David", and he was just as abusive as John is. David attacks Jane and kills her. Jane had physically fought with John, so HIS dna is under her nails, but yet David surprised her from behind and bashed her head in. So none of his dna on her body. Now, David's dna is found in her house, because he goes there to see his kids, so Jane's neighbors know it's normal to see David coming and going to and from Jane's house.
The witnesses who saw Jane fighting with John on the sidewalk, talk to the cops and give their testimony. John's fingerprints are found on the bat that killed Jane, because he owns it, uses it to play ball with Jane's kids, AND because his prints are the ONLY ones found on it, because David wore gloves while handling the bat to kill Jane. So John gets arrested because they have his prints on the murder weapon. Meanwhile, David has set up a rock solid alibi for where HE was when Jane was killed, because he knows he'll be a suspect, because the ex or husband is who they look at first. Cops know he had violent history with Jane, yet none of his DNA is on the murder weapon, so he is exonerated while John gets sent to prison because, for one, he has no alibi for the time Jane was killed, and his DNA is on the murder weapon.
This is a prime example of how and why some innocent people are imprisoned while the guilty party goes free. It all boils down to what the evidence (allegedly) shows.