Betsy wore a red dress to the library on the day after Thanksgiving in 1969. That way, no one could see the blood…
Sources:
Murder in the Stacks: 50 Years Later Still No Answers, by Erin Hogge in The Daily Collegian – Penn State https://www.collegian.psu.edu/news/campus/article_b6280ed6-1a18-11ea-a966-2b1ac6ebcdcb.html
https://www.zodiacciphers.com/betsy-aardsma-murder.html
https://pennstatermag.files.wordpress.com/2010/08/aardsma_so_09.pdf