What percentage of US mass murderers do not have a father figure in their household?
For this question, mass murder is
The FBI defines mass murder as murdering four or more persons during an event with no "cooling-off period" between the murders.
For this question, a father figure is a male member of the household who acts as the father, either married or living together with the woman, and is present for a majority of the perpetrator's life below the age of 18.
There might not be data that matches the exact definitions so best available is OK.