JMO
Interesting thoughts about the dates and possible fixation on the Friday the 13th.
Serial killers do sometimes keep track of things like that and since abduction is a crime of opportunity a lot of the times then you could be right that he may have just not been able to find a victim on the 13th and kept trying until he got his chance. Its a scary thought but possible.
The 2 girls that were killed up north I do think were killed by a real serial killer that has not yet been caught. And I always wondered if maybe the Indiana girls were killed by the same person.
Notice the date of the Indiana killings were also on the 13th. That was a Monday though but still. Maybe the number 13 is what hes after. They were found the next day on the 14th. Hmmm
"On February 14, 2017, the bodies of
Abigail J. "Abby" Williams and
Liberty Rose Lynn "Libby" German were discovered on a hiking trail in
Delphi,
Indiana,"
Murders of Abigail Williams and Liberty German - Wikipedia