The FBI believes skulls drawn in blood are the number of victims murdered by a prolific serial killer. Inside the FBI's search to identify them. "48 Hours" correspondent Peter Van Sant reports. Watch more full episodes of "48 Hours" on Pluto TV. #48hours #crime #mystery True crime. Real justice. "48 Hours" investigates the most intriguing crime and justice cases that touch on all areas of the human experience including greed and passion. "48 Hours," which premiered in 1988, has developed a rich history of original reporting and impact journalism that has helped exonerate wrongly convicted people, caused cold cases to be reopened and solved, and along the way changed lives. Subscribe to the “48 Hours" YouTube channel: null Watch full episodes of “48 Hours”: https://www.cbs.com/shows/48_hours/ Listen to the "48 Hours" podcast: https://link.chtbl.com/48-Hours Listen to the "My Life of Crime with Erin Moriarty" podcast: https://link.chtbl.com/CBSNewsMLOC Follow “48 Hours” on Instagram: https://www.instagram.com/48hoursCBS/ Like "48 Hours" on Facebook: http://on.fb.me/1KkQuRn Follow "48 Hours" on Twitter: https://twitter.com/48hours Subscribe to our newsletter: http://cbsn.ws/1RqHw7T Download the CBS News app: http://cbsn.ws/1Xb1WC8 Try Paramount+ free: https://bit.ly/2OiW1kZ For video licensing inquiries, contact: licensing@veritone.com