Role forensic psychologist play in assessing the intellectual disability

I’m 20 years old and I am intellectually disabled. I have an IQ of 55. After watching a Sponge Bob Square Pants cartoon in which Sponge Bob is hit on the head with a hammer and begins to laugh, I picked up a hammer and hit my sister over the head several times. I expected her to be like Sponge Bob and laugh like they do in the cartoons, but she never did. I miss her an awful lot and would never do anything like that again.
What role does the forensic psychologist play in assessing the intellectual disability of an individual?
What is the relationship between the forensic psychologist and the probation officer when recommending alternatives to prison?