"What are some ways to prove that someone was coherced into writing a confession for something they didn't do?

Answer 1

Now adays many police departments require interrogations to be videotaped so that if a question like this arises and independent party can make just such a determination. In the absence of this type of evidence, there needs to be testimonial evidence about the conditions leading up to the confession, like how long had the person been deprived of sleep, food, water. etc. Also, if it is alleged to have been written by the confessor when in fact someone else wrote it and the "confessor" just signed it, a content analysis can be done to see if the language and construction used in the confession is consistent with the alleged confessor's skill level and usage.

Answer 2

Have Jesus, the Pope, George W., Dick Cheney and Billy Graham say they saw the cop do it. Then MAYBE the judge would believe it.

Answer 3

i had this problem....apparently if they have your signature, thats all that counts. no one really seems to care how they got it as long as they got it.
i made such a fuss to my lawyer that he went to the judge and explained that i had signed unwillingly. they debated over it, and eventually had the paper thrown out of court.