Gein said he is aware that some family members of victims of these killers are hurt and angered about what he does for a living.
"While they do have a right to speak out against me, they don't have a right to try to shut me down," Gein said. "I run a legal business and I'm catering to a market that is in demand. I'm not a monster. I can't say I understand their pain because I'm not in their position."
One woman who has spoken out is Dee Sumpter of Charlotte, N.C., whose daughter Shauna was killed by serial strangler Henry Wallace.
"The way he killed Shauna was a personal killing," Sumpter told ABC News' Charlotte affiliate WSOC-TV. "It was with his hands, and the unmitigated gall of him to sell a photo or an artist rendering of such—I don't have words."
A sketch of Wallace's hands is on sale online for $100.
"Have a conscience. Have a heart. Have a mind," Sumpter pleaded. "Legislatively, I know there has to be something that can be done to stop this."
Unfortunately, as Kahan has found, passing legislation is difficult because, technically, these vendors are not doing anything illegal.
"Son of Sam" laws keep criminals in many states from profiting from their crimes through books, movies or television shows, but in these murderabilia businesses, it is a third party selling the items, which is legal. And if the vendors choose to send money or gifts to the imprisoned criminals, that is their choice.
"Unfortunately, they're correct. It's legal," Kahan said. "I'm a firm believer in free enterprise and capitalism, but you should not be able to rob, rape and murder and then turn around and make a buck from it. It's that simplistic."
Kahan has twice attempted to file a federal law that would prohibit the selling of these goods but has not been able to get a hearing.
Tod Bohannon, who runs Murder Auction, defends not only his business, but the criminals as well.
"A lot of people think these inmates are sitting around eating donuts all day, drinking Coca-Cola and laughing about their crimes," Bohannon said. "A lot of these guys are remorseful and they're doing the time for what they've done. Why should we continue to humiliate them?"
Bohannon does concede that not all of the criminals are remorseful, with some writing letters proudly spinning stories of their crimes, he said.
Bohannon said that while he does not pay the inmates for any of the items they send, he does not deny sending them money. He said there is one inmate that he sends $20 to every week.
Kahan takes no comfort in these explanations and continues to fight against the sales. Eight states have notoriety for profit laws that prevent criminals from profiting from the sale of personalized items, but these laws are often difficult to enforce. Since buyers are often from different states, or even countries, the transactions turn into matters of interstate commerce.
Still, Kahan says he continues to fight because he so passionately believes these businesses should be illegal.
"From a victim's perspective, nothing is more nauseating and disgusting than finding out that the person who murdered your loved one is hocking items to make a buck," Kahan said. "It's like being gutted all over again by the criminal justice system."