Betsy wore a red dress to the library on the day after Thanksgiving in 1969. That way, no one could see the blood…

Sources:

https://medium.com/crimebeat/stabbing-in-the-stacks-the-unsolved-murder-of-betsy-aardsma-5c19a50d8060

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