The Menendez brothers — who were given a new shot at freedom 35 years after gunning down their parents — have been working on a beautification project in prison that’s designed to mimic the more humanitarian conditions in the Norwegian penal system.

Erik and Lyle Menendez, convicted of the 1989 shotgun murder of their parents, have been trying to improve the San Diego prison where they’ve been incarcerated for the past six years and are serving life sentences. Prior to that, the killer siblings had been in separate facilities since 1996.

In 2018, Lyle, 56, launched an initiative called Green Space, at the Richard J. Donovan Correctional Facility. His younger brother, Erik, 53, is the lead painter for a massive mural illustrating San Diego landmarks.

Scenes of “America’s Finest City” will eventually cover the inside perimeter of 40-foot concrete walls inside the prison’s Echo Yard.

“This project hopes to normalize the environment inside the prison to reflect the living environment outside the prison,” Pedro Calderón Michel, deputy press secretary for the California Department of Corrections and Rehabilitation, said Friday.

The brothers are awaiting resentencing after spending more than 30 years behind bars for the grisly slaying of their parents, Jose and Kitty, in their ritzy Beverly Hills mansion. The case captivated the nation and spawned Ryan Murphy’s popular Netflix series three decades later.

Green Space borrowed from the design of Norwegian prisons. Norway believes in a more humane system of incarceration, which involves giving inmates more rights and nice environs in which to live.

Small prisons dot the countryside, which permits inmates to serve their sentences close to home, said Kristian Mjåland, a Norwegian associate professor of sociology at the University of Agder in Kristiansand.

There are roughly 3,000 people imprisoned in Norway, he added, which means the nation’s per-capita incarceration rate is roughly one-tenth that of the United States.

Norway has some of the world’s lowest levels of recidivism. Statistics show the number of people reconvicted within two years of release in 2020 as 16%, with the figure falling each year.

Mjåland said the philosophy guiding Norway’s incarceration system is that inmates should be treated decently by well-trained staff and have the chance to engage in meaningful activities during the day.

Terrorist Anders Behring Breivik, who killed eight people in a 2011 bombing in Oslo and gunned down 69 others at a camp for young left-leaning activists, has a dining room, fitness room and TV room with an Xbox. His cell — which he shares with parakeets — is decorated with a poster of the Eiffel Tower.

Green Space’s ultimate goal at the prison is transforming its yard “from an oppressive concrete and gravel slab into a normalized park-like campus setting surrounded by a majestic landscape mural,” according to the project’s website.

The final product will include outdoor classrooms, rehabilitation group meeting spaces and training areas for service dogs.

Attorney Mark Geragos, who represents the brothers, said he believes Lyle Menendez learned about the Norwegian model during his university classes. He is currently enrolled in a master’s program and has studied urban planning and recidivism.

With Post wires