I did some digging and it looks like Alvin Terry Duggan might have been adopted (unfortunately there isn't anything to indicate who he was adopted by/their relation to him). In 1948, when he would've been around 3 years old, a notice appeared in the Tampa Tribune
that a "final decree" had been issued "in adoption of Alvin T. Duggan."
I saw that too and would have to see if the adoption records are still available, sometimes they are destroyed but they may have some on microfilm. In Florida you cannot get a birth certificate unless you are family or if 100 years has passed since the birth, that would give us the birth parents name but we would need a family member to help. What I was able to find is that Alvin Terry Duggan born circa 1948 his parents, I assume adoptive, were Pauline C. Duggan (born June 8, 1914 Winterville, GA died Oct 5, 1998 Tampa, FL) and Jack Benjamin Duggan (born Dec 8, 1912 Tift GA died Sept 30, 1978 Tampa FL). He had one sibling Paula Kay Duggan born in 1965 that was married to to Paul Cardinal then divorced and then married Michael Lee Timmons, from what I can tell she still lives in Clearwater, FL.
It appears Alvin was married numerous times as there are several divorce and marriage records filed against Alvin Terry Duggan a rather unique name:
Alvin divorce Priscilla A Duggan Feb 1968
Alvin divorces Shirley J C Duggan July 1969
Alvin marries Alexis G. Yerby nee. Godwin on Jan 2, 1970 in Hillsborough County, FL
Alvin married Dolores Charlene Alexander June 9 1972 in Orange County Florida. Divorced April 25, 1974
Alvin divorces Deborah Ann Arciero Duggan March 5, 1976
Alexis was married to Richard Lee Yerby but divorce him in Aug 1969 in Pinellas County, FL. I was also able to locate where Alexis's parents adopted the 10 month old child in 1972. She has since relocated and changed her name and out of respect for her I will not publish her information.
Does anyone think the Virginia Johnson connection is worth pointing out to the investigator? Could there be more women that he brutalized? Now that he is dead will it solve anything or just open old wounds?