Broken glass cannot penetrate the monster's petrified skin, yet he can be given a shot with a hypodermic needle.
Dr. Rogers attempts to do an autopsy, which is interrupted. It is very unusual for a psychiatrist to do an autopsy. Only a forensic surgeon would attempt such.
Dr Rogers is only doing the autopsy because he has been refused permission by the prison authorities to send the body for autopsy to the proper people. Since he believes that the death is suspicious, he examines the body in secret as his only option for finding evidence.