Was serial killer Israel Keyes' artwork a murderous calling card?

The haunting 2012 disappearance of Samantha Koenig, an 18-year-old Anchorage barista last seen leaving her place of work with an unknown man on a dark winter night, set off a hunt that would lead the FBI and police from Alaska’s wilderness to the remote forests of Washington’s Olympic National Park, all the way to rural Vermont, exposing a killer’s terrifying trail of crimes.

The case would become the most shocking serial killer story that has remained mostly unknown until now.

As investigators followed the twisted clues in this case, they uncovered the identity of Israel Keyes, a psychopathic serial killer with a hidden life of violence and a dark path he forged while growing up off the grid. Ultimately, a search of Keyes’ prison cell reveals what investigators believe to be the chilling truth.

When authorities caught up with Keyes, they quickly learned he had killed at least three people. But the jailhouse discovery would later lead investigators to wonder whether Keyes could be responsible for murdering as many as 11 people.

Keyes, who was born in Utah, did not fit the familiar serial killer profile: he lived with his girlfriend and daughter, he owned a construction business and did not target his victims based on certain criteria, like race, gender or age.

He admitted to law enforcement that he had murdered one woman in Alaska and a couple in Vermont. He said he had set certain goals for himself, and the murders fit into accomplishing those goals. He also admitted to police that he had fantasies about killing people in a carefully constructed murder plot.

"Keyes definitely talked about the hunt, how the urge would come about him and then he would, he would plan a trip and a homicide would happen," FBI Special Agent Joelene Goeden said. "It was a hunt for him, a hunt for kind of that perfect situation."

Years in advance, Keyes buried kill kits --- items he could eventually rely on to murder victims across the continental United States --- to complicate tracking his movements leading to his crimes. He would bury these kits so they were ready for his next homicide. In New York, Keyes stowed a .22-caliber Ruger weapon without a stock, empty magazines, ammunition and a silencer in a watertight bucket, according to the FBI.

After he was caught, Keyes spoke of killing other people and, while in jail, officials discovered he used his own blood to draw 11 skulls, which authorities thought might represent 11 victims.

"Wild Crime: Eleven Skulls," the ABC News Studios' true crime series that explores the intriguing case of Keyes and his potential unsolved murders, premieres Dec. 5 on Hulu.

Keyes abducted the 18-year-old Koenig on Feb. 1, 2012, while she was working as a barista at the Common Grounds Espresso coffee shop in Anchorage, Alaska.

Keyes never met Koenig before that day and told police he only went there because the shop was open late.

"He didn't know who was going to be there before he got there," FBI Task Force Officer Jeff Bell said. "He assumed it would be a young girl."

Keyes took Koenig to his home, where he lived with his girlfriend and daughter, and locked her in a shed on the property. He took Koenig's cellphone and debit cards, then texted her boyfriend from her phone, making it seem like she was OK. He also asked Koenig for her debit card PIN and stole funds from her.

Then Keyes murdered Koenig.

Just a few hours after the murder, Keyes woke up his young daughter. They flew to New Orleans, where his girlfriend would join him the following day to begin a family cruise – leaving Koenig’s dead body in his shed.

"This is one of the worst details of all that someone raped and murdered a teenage girl in his shed at his home and, when he's done, goes back inside to his live-in girlfriend and small daughter and hours later takes them on a cruise," said journalist Maureen Callahan, who chronicled Keyes' case in her book, "American Predator: The Hunt for the Most Meticulous Serial Killer of the 21st Century." "Pure evil."

The events that followed, including how Keyes tracked media coverage while on vacation, set up a ransom demand that included a macabre “proof of life” photo, the discovery of Koenig’s remains and Keyes’ arrest and subsequent confession, reveal the mindset of a twisted serial killer whose motive had yet to be fully revealed.

Keyes was arrested on March 12, 2012, and initially charged with theft and using a stolen debit card. However, after FBI agents raided his home, Keyes confessed to murdering Koenig.

Keyes also admitted to murdering Bill and Lorraine Currier, a long-time couple in Essex, Vermont. He told police he shot and killed the husband then he sexually assaulted and murdered Lorraine.

"It had been 10 months since Bill and Lorraine had been reported missing," Vermont State Police officer Lance Burnham said. "You stop seeing the tips come in and then all of a sudden other cases come in, but it's still on your mind every day."

Keyes seemed eager to tell police his stories. He would eventually be on trial for the murder of Koenig but the trial got delayed and, in the meantime, Keyes left something intriguing.

He sketched a series of 11 skulls, drawn in his own blood, which were found underneath his bed in his jail cell. This led law enforcement authorities to wonder if Keyes was documenting how many victims he killed.

"I believe this signifies Satan and Israel Keyes and the upside-down crucifixes on his 11 victims indicate that these are his and these stories and souls belong to him," Bell said. "And we'd like to put a name to each one of these."

Police worked to confirm their theory as Keyes worked to make sure that investigators might never learn the truth.