How morally responsible are severely traumatised people or those with brain injuries for their behaviour?

I recently went down a rabbit hole about Fred and Rose West, the serial killer couple from the UK, and what stood out to me was how deeply traumatic both their childhoods were.

Fred allegedly began being abused by his mother at age twelve, and his father reportedly encouraged him to engage in acts of bestiality. Rose’s father also abused her as a child and later paid for her services when she became a sex worker.

Both also had physical factors that might have influenced their psychology. Rose’s mother underwent electroshock therapy while pregnant with her, and Fred suffered multiple head injuries growing up. I’ve read that around 80% of high-profile serial killers have a history of brain trauma.

All of this got me thinking:
To what extent can people like this be considered morally responsible for their actions, versus being products of their circumstances and neurological damage? At what point does trauma or brain injury reduce, or even eliminate, moral responsibility?