I'm not qualified to have a strong opinion, but I know one very interesting criminal case. In fact, there are many. But there's a guy called Thomas Dee Huskey aka “Zoo Man (https://www.bizarrepedia.com/multiple-personality-disorder)

A serial killer who killed prostitutes. He was described as dumb as a box of rocks, but his other personality, who allegedly committed the crimes, was left-handed. It's extremely difficult to fake it, even if you have high IQ. The handwritings experts agreed they are handwritings of "two different persons". There were many other facts I can't remember right now, but even the prosecutor agreed this guy probably has DID. And that's rare...