rwl, seriously?  Our (and every other) government kills innocents all the time.  Per Wikipedia, 1,400 offenders have been executed since 1976.  The US killed an estimated 170,000 innocents in the Iraq war alone, perhaps 98,000 civilians in Syria, etc.  The numbers are likely wrong, but I'd bet they are in the ballpark.  We try not to kill innocents, but war and punishment are messy affairs and innocents die.  The question is, what policy gets the job done with the least amount of innocent deaths?  

https://en.wikipedia.org/wiki/Wrongful_execution
https://en.wikipedia.org/wiki/Casualties_of_the_Iraq_War
https://en.wikipedia.org/wiki/Casualties_of_the_Syrian_Civil_War