Why did Dahmer drill holes in people’s heads?

Dahmer drilled holes to deaden a portion of their brains and poured fluids into their skull. This was said by Fredrick Fosdal, hired by prosecutors to examine Dahmer.

Fosdal said Dahmer had told him he drugged his victims and performed the brain operations while they were unconscious.

Fosdal was hired to examine Dahmer after the body parts of 11 males were found in his Milwaukee apartment in July,

Dahmer also admitted to the police that he killed and mutilated 17 males and pleaded guilty but insane to 15 of the killings.

If insane, Dahmer could be sentenced to a mental institution where, after a year of treatment, he could petition for release every six months.

Fosdal said he found nothing in his examination of Dahmer to support the insanity plea.