Mary Margaret Guilfoyle was a 24-year-old college student who was murdered on October 24, 1972, in Santa Cruz County, California. She was last seen hitchhiking to an interview and was picked up by Herbert Mullin. Mullin stabbed her to death during the drive, partially dissected her body, and scattered remains in the Santa Cruz Mountains. Skeletal remains were found February 11, 1973, near Bonny Doon.

Investigators initially considered Edmund Kemper as a possible suspect, but subsequent work identified Herbert Mullin as the killer; Mullin later confessed, saying he believed human sacrifices would prevent earthquakes and that voices instructed him. Mullin was arrested February 13, 1973, after a series of Santa Cruz area murders and was convicted on multiple counts, receiving a life sentence.

Did anyone who knew Mary in 1972 ever notice her planning to hitchhike that day or expecting an interview?