Inside the investigation of a prolific serial killer and the FBI’s mission to identify his unknown victims.

These skulls, drawn by serial killer Israel Keyes in his own blood, were found under his bed in his jail cell. The FBI is making them public for the first time. It is believed Keyes killed 11 people, as represented by the 11 skulls.

Israel Keyes

A mug shot of 34-year-old Israel Keyes.

During an interrogation Keyes told law enforcement, “Once I started, you know, there was nothing else like it.”

Samantha Koenig

Samantha Koenig, 18, was abducted on February 1, 2012. According to reports, the reward for her return reached $70,000 by February 28, 2012.

The Coffee Stand

The Common Grounds Espresso coffee stand in Anchorage, Alaska, where barista Samantha Koenig disappeared on February 1, 2012

Texas ATM Withdrawal

Investigators were monitoring Samantha Koenig’s debit card and were alerted after an ATM withdrawal was made from her debit card in Sheppard, Texas. Israel Keyes is seen here on surveillance video with a hood, sunglasses and a face covering.

Keyes’ Rental Car

Israel Keyes would often rent cars when he traveled and then drive thousands of miles to locations where he wanted to kill. He was driving a rented white Ford Focus when Texas officers pulled him over for a traffic infraction. After searching the vehicle, they found an ID, debit card and cell phone that belonged to Samantha Koenig. He was arrested.

Keyes Questioned

Israel Keyes was questioned at the FBI’s Field Office in Anchorage, Alaska. Keyes confessed he murdered Samantha Koenig to members of the Anchorage Police Department, U.S. Attorney’s Office and FBI agents. The interviews from that confession have never been made public.

Keyes’ Home in Alaska

The Alaska home of Israel Keyes and the shed on the right where he killed Samantha Koenig.

Recovering Samantha Koenig

Divers at Matanuska Lake in Alaska recovered Samantha Koenig’s body on April 2, 2012.

Keyes’ Confession

Assistant U.S. Attorney Frank Russo, left, with “48 Hours” correspondent Peter Van Sant in the conference room where Israel Keyes admitted to killing Samantha Koenig.

Bill and Lorraine Currier

Bill and Lorraine Currier were chosen at random by Israel Keyes and abducted from their Essex, Vermont, home on June 8, 2011. They were taken to a farmhouse and murdered.

The Curriers

A photo of Bill and Lorraine Currier with yellow ribbon  draped on a tree was posted outside of their home in  Essex, Vermont. The photo was taken on December 29, 2011, when the fate of the Curriers was still a mystery.

Currier Crime Scene

Broken glass from the interior garage door where Israel Keyes broke into the Currier’s home in Vermont. Photos were taken by investigators on June 10 and 11, 2011.

Currier Crime Scene

Investigators examine the broken glass at the Currier home in Essex, Vermont.

A “Kill Cache” Recovered

What Israel Keyes called a “kill cache” is seen buried at the Blake Falls Reservoir in Adirondack Park in Parishville, New York. Keyes would bury caches with weapons and tools across the country. Whenever Keyes got the urge to kill, he would dig up a cache he had buried years prior and retrieve the murder weapons to commit his crimes.

Keyes’ Kill Kit

A Home Depot bucket filled with weapons and tools recovered from the Blake Falls Reservoir in Adirondack Park in Parishville, New York. The FBI believes Keyes buried caches like this throughout the U.S. If a member of the public finds one, the FBI says do not touch it. Call the FBI at 1-800-CALL-FBI or visit https://www.fbi.gov/tips.

“Kill Cache” Weapons

From left, FBI Special Agents Katherine Nelson and Jolene Goeden and  “48 Hours” correspondent Peter Van Sant look at weapons recovered from Keyes’ kill kits or caches at the FBI Field Office in Anchorage, Alaska.

Julie Harris

Julie Harris was 12 years old when she disappeared from Colville, Washington, on March 3, 1996. She was a double amputee whose prosthetic feet were found by the Colville River a month after her disappearance. Israel Keyes, then 18, lived in the area at the time. Julie’s murder is still unsolved.

In the Military

Israel Keyes in 1999 at the Air Assault School graduation, Fort Lewis, Washington. Keyes was enlisted in the U.S. Army from July 9, 1998  through July 8, 2001.

Keyes’ Boat in Washington

FBI Special Agent Ted Halla and Peter Van Sant at Lake Crescent in Washington State. The FBI believes Israel Keyes killed four people in Washington. “He had a boat. We know that he took it out on this lake… along with some of the other lakes in the area. He revealed to us that one of the Washington State victims was actually — their body was sunk in this particular lake,” Halla explained.

Tracking Keyes’ Travels

FBI Special Agent Katherine Nelson and Peter Van Sant look at a timeline of Israel Keyes’ travel activity from 1997 to 2012. Investigators believe it’s possible there may be victims everywhere he traveled during that time.

Debra Feldman

The FBI believes Debra Feldman is the fourth known victim of Israel Keyes. Feldman was last seen alive on April 8, 2009 at her residence in Hackensack, New Jersey. At the time of her disappearance she was 49 years old. Investigators are still trying to identify Keyes’ remaining seven victims.

A Suicide Note

A note found in Israel Keyes cell on December 1, 2012. Investigators say it’s full of rants, but gives no information on his crimes or other victims.

Remembering the Victims

A memorial plaque dedicated to Samantha Koenig and all of Keyes’ other victims, located on a gazebo at Matanuska Lake in Alaska.

“This case is about them and their lives and the lives that they have not been able to live and the families who no longer have them there,” said FBI Special Agent Jolene Goeden. “That’s what this case is about. It’s not about him. I try not to focus on him.

To report tips about the Israel Keyes case, call 1-800-CALL-FBI or visit https://www.fbi.gov/tips.