The courts should allow the 10 guilty felons go free if there is a legal technicality. But, actually it depends on the situation. If someone isn't read their rights and they say something that they shouldn't say. It would then probably be used against them in court and they wouldn't even know it. They also need to know if they can have a lawyer. Everyone has rights, no matter if they did the crime or not, everyone has rights to try to protect themselves. .
Some technicalty could be excusable homicide. This is killing of human by misadventure or self-defense. This is when some evil, fault, error, or omission on the part of the person who commits the homicide. Degree of fault is not enough to constitute. So if someone did kill another human being because they were using self-defense, the victim was abusing, or trying to kill defendant, then it really can't be tried because defendant was only trying to save him or herself. Next, there is there could be lack of mens rea, which is stated as essential mental requirement. Where there is proof that the defendant acted intentionally with the highest degree of mental fault. They acted knowingly, recklessly, and acted negligently. There might not be any corpus delicit which is proof crime was commited. .
Another reason would be from lack of scienter. Which states that it is the degree of knowledge that makes an individual legally responsible for the consequences of his or her own acts. AN example would be US. V. Falu 776 F.2d 46,38 crl 2124 (1985). This is where a person sold drugs to an office with in 1,000 ft of a school. They couldn't see the school where they were though, because there were trees all around. Falu didn't know school was that close. After he was arrested he was then later let go because he couldn't see the school from where he was and the officer set him up. Also, Minnesota V. White 464 N.W. 2d 585 (1990). .
There could be legal impossibility, which states that the defendant's completed act is not a crime even though a defendant obviously intended to commit a crime.