Regardless, the scenario stands as is. The detective found your missing relative alive. Do you thank him or curse him.
No, it doesn't, because it presumes no other possibilities and is therefore a false premise. It is artificial because the cop would not be fool enough to try it under a Constitutional justice system; else he would lose the conviction. Yet to play your game by the Constitutional standard, I would thank him for my relative safety and curse him for getting the crook off with his clumsy handling of the case having produced inadmissible evidence, leaving the perp free to trouble my family and his in retaliation. Your cop would be prosecuted and land in jail. I would then console his family pursuant to the perp's calculated retribution having shot the SOB for trying it with mine.
You lack creativity, which is why you resorted to the easy, familiar, and dishonest gambit.
Citizens are not sheep. The justice system has made the people into sheep. It was not originally intended to run this way, and didn't for most of the first century of this nation's life until communist lawyers started to mess with it with the goal of a police state making citizen law enforcement virtually impossible. They succeeded. Apparently you like it that way. Unfortunately, it has made police officers perjuring themselves a daily occurrence (and yes, I do know police officers and this is from what they say, even in tony Silicon Valley).