What made it all the more horrifying: for weeks no one had any idea who was committing the crimes.
Friday evening's "20/20" special took a new look at the case, including previously unaired footage of Diane Sawyer's historic 1993 interview with Manson in prison - the last interview he has given.
The special also looked at a key piece of evidence in the investigation that was discovered by a reporter working for this station, KABC-TV, at the time.
To hear former ABC7 reporter Al Wiman discuss how he found bloody clothes discarded by the killers on a Los Angeles hillside, watch his interview with David Ono in the video above.