"Some of them are grossly pornographic. Some of them start that way and talk about erections and stuff like that. Sometimes they want to play a game but if I say 'no, don't, I'm not interested in that', I do get an apology.
"People like (American serial killer, rapist, burglar, and Satanist) Richard Ramirez, he just kept coming at me, with all of this 'I want to do this to you, I want to do that to you', and that continued until I changed post office boxes."
Amanda Howard has been writing to serial killers for more than 20 years. Despite the creepy nature of some - notably a handwritten letter from Genesee River Killer Arthur Shawcross which reads, "Do you see me at night when you sleep?" - she says her work is for a good cause; to help solve crimes.
But it also comes with a price.
"I've had 'Toolbox Killer' Roy Norris threaten to put an ice pick into my ear, which is what he and his partner had done to his victims.
"I've had a family of killers come after me a couple of times and threaten me and tell me to back off.
"They all play games, they all can switch on the charm and switch it back off. You can't show weakness, otherwise you're done. It can be really tough. You have to play the game, and sometimes you're the cat and sometimes you're the mouse. It depends who the killer is."
Sometimes, these killers send her trinkets - or locks of hair. Ms Howard shows a lock sent to her by death row inmate Bobby Joe Long, who abducted, sexually assaulted, and murdered at least 10 women in Florida. His last victim was raped for 26 hours.
It all began when a psychopath who stalked Sydney's wealthy North Shore suburbs throughout 1989 and 1990, killing six elderly women and bashing and molesting several others, became known as The Granny Killer.
The case was one of the first serial killings in NSW, but it captured the attention of investigators from around the world - and one local teenage girl.
It was 1989 and Howard was just finishing school in Sydney with plans of becoming a singer and dancer.
When police profiled the case they imagined a young, unemployed, evil skateboarder who hated his family. But when cops caught up with their killer, he was 57-year-old pie salesman, John Wayne Glover.
"It just showed how normal these people are, it was quite shocking. I was hooked," Ms Howard told news.com.au.
"They're extraordinarily normal."
But it was when Ivan Milat's backpacker murders became public four years later that the true crime author's love affair with the extreme began. Ever since, she's been delving deep into the minds of serial killers in a unique game of "cat and mouse".
"Ivan was one of my very first contacts, he was quite normal too," Ms Howard told news.com.au.
"I can see Ivan's house from mine, it's a very short walk between the two of us."
"I would have bumped into him at the shopping centre and not even known. When it's someone local and you can see the cop cars out the front, that creates that link. You go down that rabbit hole.
It set Ms Howard on a journey, where she embarked on a mission to get inside the minds of serial killers - and to discover what makes them tick. She says it's become an important part of her research for her true crime novels.
Ms Howard published her first book, River of Blood: Serial Killers and their Victims, in 2004 while her latest book, Rope, published last year, looks at the history of people who have been hanged.
These days she has approximately 55 serial killers on her letter-list, varying in age, range and notoriety. Most are from the United States, but others come from Australia and England. She says she receives about 40 letters a week from across the globe.
"I just get these people to talk," she says.
"Ivan [Milat] wrote to me last week and sent me twelve pages. It's not like he's just answering a question, I'm getting a little bit more from them than that, some of them slip up sometimes - that might create more charges."
She began with the man dubbed Australia's "sickest serial killer", David Birnie, who along with wife Catherine, committed dark, sick and sadistic sexual fantasies with their victims.
Since then she has raised the stakes and includes Charles Manson among her regular correspondents.
"That's only part of the story, there's a lot I don't tell."