According to the seller, the item is a Texas Instruments TI-83 Plus calculator, similar to thousands of others used in college-level math classes. It usually retails for about $99. This one is listed at $3,700.

What makes it worth so much? It once belonged to the man who killed 32 people at Virginia Tech on April 16, 2007.

The listing on the crime memorabilia Web site Supernaught says it is “one of the few items that the Virginia killer Seung Hui Cho sold on eBay to raise money for the guns, clips and ammo utilized during the rampage.”

The calculator and hundreds of items like it — the personal effects, paintings, letters and even fingernails of killers — are being peddled to collectors by at least a half-dozen Web sites as “murderabilia.”

Seung Hui Cho’s calculator is also a rarity. Experts and murderabilia collectors say it is the first item with a connection to the gunman to be available for purchase in more than four years — since the first 48 hours after his mass murder. It is the only item of his on the market, experts say, at a time when Virginia Tech is back in national news after the December shooting death of a police officer in Blacksburg.

The market for murderabilia is hardly a new phenomenon. In London during the late 1880s, British subjects paid admission to stand in the rooms where Jack the Ripper slashed his victims.

In the 1950s, the Ford sedan driven by killer Ed Gein, who inspired the movie “Psycho,” was paraded around county fairs and promoted as “the car that hauled the dead from their graves.”

Murderabilia can command steep prices. The handgun Jack Ruby used to kill John F. Kennedy assassin Lee Harvey Oswald was sold in a 1991 auction to Anthony V. Pugliese III, a Florida real estate mogul, for $220,000. Paintings by executed serial killer John Wayne Gacy, who murdered at least 33 boys, have been purchased for as much as $15,000.

Today, most murderabilia is sold online, making the shopping for serial killer collectibles easier than ever.

“It’s an insidious and despicable industry,” said Andy Kahan, a Houston-based victims’ rights advocate and law enforcement official who has led a nationwide campaign to prohibit the sale of murderabilia.

Although eight states, including Texas and California, have laws that prohibit convicted killers from profiting from their crimes, efforts to push legislation through Congress have failed repeatedly. Virginia, Maryland and the District permit the sale of such items, Kahan said.

Over the years, Kahan has amassed a “smorgasbord of items,” including a lock of Charles Manson’s hair braided into the shape of a Nazi swastika, purchased for about $50, and fingernail clippings of killer Roy Norris, who is imprisoned in California for kidnapping, torturing and murdering teenage girls. The fingernails cost $12.99, which Kahan described as “a bargain.”

Kahan said he uses the murderabilia for testimony and lectures on how people profit off of “heinous and diabolical crimes.” Selling the items of killers, Kahan said, “gives them infamy and immortality they don’t deserve.”

Cho’s calculator actually went on the market three months before the Virginia Tech massacre. It was put up for sale by Cho himself, who sold it on eBay for $53 plus $9 for shipping.

According to an archived eBay Web page, Cho said the calculator was “used for less than one semester then I dropped the class” and “works perfectly.” It also came installed with games such as Bomberkids, Mars Patrol and Sub Hunt, he added.

Not long after the shootings, Kahan said, more than 100 items once owned by Cho — including textbooks he used in classes — appeared on eBay. To prevent the dissemination of the materials, Kahan bought transcripts of a few of Cho’s violence-themed plays for about $20 each.

Tod Bohannon, who runs the Web site Ghoulslikeus, said he was offered the calculator a few weeks after the Virginia Tech killings. The seller had papers proving that he had purchased it for about $280 on eBay from the person who originally bought it from Cho, Bohannon said. (Establishing authenticity is often a challenge for murderabilia collectors, said Steven Scouller, a Scottish researcher and murderabilia collector. “There are more fake Mansons than Picassos,” he said.)

Bohannon was convinced of the calculator’s authenticity and was interested in obtaining it for his collection. Instead of cash, he offered to trade letters written by Manson, he said. But the seller chose to accept a cash offer from Supernaught owner Ken Karnig.

Karnig did not respond to requests for comment for this story. On his Web site, Karnig says he does not grant interviews to the news media.

So who buys murderabilia? Bohannon said he has sold items to educators, journalists and college students studying criminal justice. “It’s all walks of life,” he said.

Kahan said collectors are often younger men who purchase letters or artwork. Creative pieces, he said, allow buyers who idolize high-profile killers the chance to “own a piece of their soul.”

Even government sometimes participates in the industry. In June, California auctioned a number of items once owned by the Unabomber, Theodore Kaczynski, including a Smith Corona typewriter that sold for $22,003. The National Museum of Crime and Punishment in Northwest Washington bought a scale and tools Kaczynski used to build his bombs in the auction, spending about $1,100. The proceeds of the auction went to his victims’ families.

That is not the case with the calculator. Leah Palmer, whose sister Julia Pryde was killed by Cho, said Karnig “is trying to profit off of what this guy did.”

“The question is, what’s he doing with the profit? Celebrating Christmas or doing good for society?” she said.

Not all are convinced of the calculator’s appeal to collectors. “It doesn’t have any obvious connection with Cho or the crimes he committed, which makes it less appealing,” said University at Buffalo professor David Schmid, who wrote the book “Natural Born Celebrities: Serial Killers in American Culture.”

For now, the calculator remains unsold. Listed for months, it has had no takers.