It’s a relaxing image. A bouquet of tulips stuffed into a golden pitcher. Their colorful buds, rich with yellow and blue, stand erect above a cluster of perfectly detailed greenery. A kitten playfully paws the air below the arrangement while a dainty mouse sneaks around the vase.

As serene as it seems, it came from the mind of Charles Ng, who abducted and murdered families all across northern California from 1983 to 1985.

Ng, along with Leonard Lake, were responsible for some 25 murders where they would keep the women alive and kept as sex slaves, often videotaping the acts.

Ng’s painting is one of many artworks listed on the art website Murder Auction, which is billed as the “world’s leading true crime memorabilia auction house.”

Perusing through the listings, it’s easy to compare the artistic findings to that of any amateur online community. Unfinished renderings, messy compositions, and lofty doodles stream one after the other for some pretty high prices.

A cartoon sketch of a French-speaking Humpty Dumpty can be yours for $50.

It looks cute, like something that may appear in a child’s bedroom or in the Sunday Funnies. But the artist, Michel Fourniret, murdered at least nine females throughout the 80s, 90s and 2000s, so there’s that to consider.

Or maybe a rather surrealist-looking portrait is more your taste?

Four mixed-race faces are molded and morphed into one center being. It’s better quality and a little pricier ($950), but does comes with Satanic imagery smack dab in the middle—horns sprout from the figure’s head and melds with the shirt collar of another half-drawn man.

Oh, and it may or may not have been painted with the artist’s own blood. Dr. Jack Kevorkian, who assisted more than 130 suicides, was known to do just that. And this is one of six that were released in the mid-1990s.

Then, there’s a pretty unskillful looking psychedelic painting filled with crosses, swastikas and a lot of angst. The $1,200 price tag seems a bit steep for something that could have been painted by an 8-year-old. But isn’t that how we all feel about modern art?

It’s one of the most expensive listings—partly due to the fact that it’s signed “Charles Manson,” the notorious cult-leader responsible for the 1969 murders of actress Sharon Tate, her unborn baby, and six other people in Los Angeles.

Hundreds of similar artworks by notorious murderers fill page after page of listings. And Murder Auction isn’t the only one offering up the goods. There’s also Supernaughtf, Darkvomit, and Serial Killers Ink.

After eBay’s decision in 2001 to ban all sales of “murderabilia,” or collectables used or owned by convicted murderers, the market was forced underground.

The clause also includes disasters and human tragedies, terrorist organization and hate groups, items related to violent felons, and Nazi or Nazi-related material. Thus, a slew of websites spawned and began to dominate this niche market.

“It’s definitely a very interesting topic,” William Harder, the proprietor of Murder Auction, told The Daily Beast. “There’s tons of public interest in this. You’re not doing a story on it because it’s not interesting and there’s a reason why there are more books written about serial killers than U.S. Presidents.”

Seasoned television shows like Bates Motel, The First 48, and even HBO’s The Jinx based on the recently arrested Robert Durst, all delve into the minds and actions of killers while an entire category of crime documentaries has a home on movie streaming services like iTunes and Netflix.

“These are just interpretations of the criminal,” Harder continues. “You are hearing the people who put the documentary together and they are basically saying the facts. There are people that just collect case files and court transcripts to get to the truth while some people decide they want something personal. And why wouldn’t that happen? It happens with movie stars.”

Harder’s own interest began when he was just a teenager and he began reading about Sean Sellers, who murdered his mother and stepfather in 1986.

“He was 16-years-old and I was around that same age,” Harder said. “I just couldn’t understand how somebody could kill their own parents and the interest in [true crime] just grew from there. Eventually I discovered there were websites dedicated to this sort of artwork and began writing to my first serial killer.”

Four years after penning a letter to Richard Ramirez, the “Night Stalker” serial killer who terrorized the Los Angeles and San Francisco area in the mid-1980s, Harder was visiting him at San Quentin State Prison in Northern California. The first letter he received from Ramirez on November 15, 2000, was his first piece of “murderabilia.”

Since then, he’s visited some seventy convicted murderers, including Charles Manson, amassing an impressive collection of artworks and collectables that attracts people from all over the country.

Last month, over Valentine’s Day weekend, Harder packed his goods and headed to Chicago for the Mad Mobster True Crime & Horror Expo, where he exhibited the best items he’s acquired from over the years—poetry by Jeffery Dahmer, a self-portrait by Lee Boyd Malvo, and string art by Charles Manson.

“Manson gave me one of his string art spiders, which is probably my favorite,” Harder said. “I had a guy at the Mad Mobster show offer me $6,000, but I had to say, ‘Sorry, man. It’s not for sale.’”

Kane Hodder, the actor who portrayed Dennis Rader in the film BTK, was in attendance. So was John Wayne Gacy’s childhood friend (Gacy was the “Killer Clown” that murdered at least 33 teenage boys in the 1970s).

Harder even befriended a survivor from the Columbine High School shooting and a cop dressed as Leatherface, the skin-wearing character from Texas Chainsaw Massacre, which was inspired by real-life killer Ed Gein.

Recently, the California Department of Corrections filed a search warrant for his property in connection with four inmates they believed he was paying for their art.

This would violate the “Notoriety for Profit” law (originally enacted as the “Son of Sam” law in New York) that prevents convicted killers from profiting off their notoriety.

Harder insets that he has never paid inmates and the news crew that came to his home to see if the accusations were credible discovered just that. “They said, ‘None of these items are addressed to you.’ And I said, ‘Of course they’re not. I don’t sell items sent to me.’"

There are seven states that have laws prohibiting inmates from directly profiting from their crimes, Harder explains. He believes they should be allowed to if it’s purely for artistic purposes.

“If Charles Manson painted a picture of a bouquet of flowers sitting in a vase, he should have every right in the world to sell that. But, if Charles Manson painted a portrait of Sharon Tate,” then that would be unacceptable.

In 1997, Elmer Wayne Henley, who tortured, raped, and murdered 28 teenage boys in Texas during the early 1970s, held his first public art exhibition curated by his pen-pals.

He refused to create anything profane or obscene, instead sticking to serene landscapes and still lives. Proceeds were donated to this prison system, his mother, and himself.

And true crime fanatics aren’t the only ones shopping for killer art. So are law enforcement agents, government officials, and researchers.

“I’ve had three law enforcement agencies buy letters from me,” Harder said of having cops browsing his website. “Two were in the United States and one was in the UK. They usually buy about $200 worth of letters all from low profile killers.”

The UK agents “buy these things whenever they want to do something fun” while the United States government agencies “both said they were doing handwriting analysis.”

Even scholars use his site for their research. One professor, who studies the behaviors of school shooters, purchases a large amount of personal letters that come up for auction.

“He’s bought me out of all the Michael Carneal items,” Harder said of the then 14-year-old Kentucky shooter from 1997. “He’s doing research to figure out why this happens and he’s buying up letters to further his research.”

As for the families of criminals and victims, they have both been supportive of Harder’s endeavors. Sean Sellers’ biological father, Richard, who would have been killed had Sellers reunited with him, gave Harder an entire collection of letters and personal items from his son.

“He said, ‘If you can make money off these to further your visits then do it because I believe in what you’re doing.’” Harder explained. “That meant a lot coming from a victim.”

Sean had planned to kill both of his biological parents, according to Harder. “He was trying to get back to California to be in his father’s custody where he would have ultimately killed him as well. So to have a victim come to me and say, ‘You’re doing something good with this. Take it.’ I was completely floored.”

But not everyone is as supportive.

“I receive death threats monthly,” Harder revealed. “They usually come in the form of e-mails to the website, and now Facebook. People tell me they wish my mother was murdered, they wish my sister was raped and murdered. They even say they wish my kids were getting murdered so I could understand the pain.”

“One guy said, ‘If I could find you, I would skin your kids alive in front of you and drag them behind a truck for you to watch.’ That’s probably the most creative death threat I’ve ever gotten.”

Still, Harder continues to collect, trying to remain as anonymous as possible to shield his loved ones and keep them out of the limelight. “If someone is actually going to come and openly hurt me, then they’re going to come. We will cross that bridge when we get there.”

And while Harder believes that people should be allowed to collect and sell what they want, he does restrict the site from becoming a free-for-all.

He doesn’t allow any photographs of a victim’s children or of an offender’s children, any item directly related to the cemetery burial plot of a victim, and any item directly related to the victims of 9/11.

“My site is the largest and I had to draw the line in the sand somewhere,” Harder said. “But, you have to understand that a lot of these guys committed these crimes thirty years ago. Just think of yourself ten years ago. Are you the same person now? Some of these guys have had 40 years to sit in a box and think about what they did and a lot of them are ashamed.”

So, they compartmentalize their actions, use art as way to move forward, and give avid collectors new works to pursue.