He was convicted in 1996 of first-degree murder with special circumstances (burglary, robbery, kidnapping, and an attempted lewd act upon a child under the age of 14) of 12-year-old Polly Klaas.

As of January 2024, Davis remains on California's death row in the Adjustment Center at San Quentin State Prison.

Davis is of partial Northern Paiute heritage through his maternal grandmother, Norma Wasson Johnny, with whom he and his family lived for a time before his father moved them into a house in La Honda.

[1] His early life was disadvantaged; both parents were violent alcoholics[2] and his mother had once punished Davis and his brothers for smoking by burning their hands on a hot stove.

[4][5] He witnessed many violent domestic disputes between his parents, who separated when Davis was nine, leading his mother to take him and his siblings back to their maternal grandmother.

Robert, a longshoreman, was frequently unable or unwilling to care for his children, so he had them shuttled among family members, hired caretakers, and women he was romantically involved with.

[8] At 17, when Davis was in court for a motorcycle theft, a judge told him that he could either go to the California Youth Authority or join the United States Army.

Within hours of the kidnapping, in a rural area of Santa Rosa, about 20 miles (32 km) north of Petaluma, a babysitter on her way home noted a suspicious vehicle stuck in a ditch on her employer's private driveway.

A review of calls in the area the day of the kidnapping turned up the contact with Davis, who had only been identified because both deputies had filled out and filed the FI card.

The Sonoma County Sheriff's Department, in cooperation with Petaluma Police and the FBI, launched a search of the property and the Pythian Road area during a heavy rainstorm.

When nothing was found during the initial search and the surveillance of Davis also produced no results, the decision was made to arrest him for the kidnapping of Klaas.

Although Davis admitted to strangling Klaas to death, he refused to give investigators a timeline of the events from October 1.

It is believed that Davis killed Klaas before the arrival of deputies and hid her body in the thick brush on the hillside above where his car was stuck.

He was reportedly out of breath, sweating profusely, despite it being a cool night, and had twigs and leaves in his hair when contacted by deputies.

Davis had to drive from the Indian Rancheria in Ukiah once a week to meet with his parole officer and he would have seen any police activity in the area.

After the verdict was read, Davis stood and made an obscene finger gesture at the courtroom camera with both hands.

An enraged Marc attempted to lunge at Davis but was restrained by the bailiffs, leaving the courtroom to avoid causing further commotion.

His lawyer, Phillip Cherney, told reporters he intended to ask for a rehearing and that he would be lodging a habeas corpus appeal with state and federal courts.

[19][20] The A&E television series American Justice released the episode "Free to Kill: The Polly Klaas Murder".

[21][22] The Discovery Channel crime series The FBI Files' first episode's topic was the Polly Klaas case.

The episode reveals the details of the FBI agents' collection of evidence and their hunt for the criminal, and originally aired October 20, 1998.

[citation needed][23] On May 9, 2022, Crime Junkie released an episode on Polly Klaas and discussed how the case set a precedent for California's Three Strikes law.