I'm a writer and, in this murder mystery I'm writing, I'm trying to see how sentencing laws would apply in this scenario. If a person was arrested for killing somebody but then it is later found out that someone else "hypnotized" or "brain-washed" that person into doing that killing, completely out of their own free will, what would happen to the "hypnotized" person? Would they still be convicted of the crime but have a substantially lessened sentence? Would they be found innocent due to some sort of defense? I know the person who did the "hypnotizing" would likely be arrested and convicted, but I wonder what would happen to the person who actually pulled the metaphorical trigger?
Intent is an element of the offense of murder. If the prosecution can't prove the required level of intent for murder, the defendant may still be convicted of a "lesser included offense" like Manslaughter or perhaps Criminally Negligent Homicide, or even an offense that doesn't require an actual death like Aggravated Assault or an offense that doesn't require proof of an injury like Deadly Conduct.
If the defendant is claiming that the intent was not voluntary because of some hypnotic effect then that is basically an insanity plea. Defendants found not guilty by reason of insanity face an indefinite commitment to a mental hospital, which can amount to decades of involuntary hospitalization. To learn more about this situation, read about the case of John Hinckley Jr.
I personally doubt any jury would actually believe a hypnosis defense, especially without a woo-woo jury foreman, some outstanding work by the defense attorney, and a team of expert witnesses that includes an unrelated hypnotist and a psychologist who didn't believe in hypnosis until examining the defendant in this case... so a Mulder and a Scully.