He's a mysterious man who now, because of 9Wants to Know's investigation, finds himself under an expanding investigation by the Parker Police Department, the Arapahoe County District Attorney's office and the Colorado Attorney General's office.
Dozens of people in the Denver area, and in at least four other states, know his name or his supposed company.
"I got a call from this Associated Management and he sounded legitimate," said Yvonne Araujo, who believes she was the first to fall for Castle's tactics in February.
Araujo filed for bankruptcy last year and expected to lose her house. She says her lawyer told her to wait for a call from her bank when her house went into foreclosure. He told her that wouldn't happen for four months, the typical time it takes a bank to foreclose.
Araujo got calls right away from a man named Greg Castle.
"Hi Yvonne, this is Greg with Associated Inspection Service. We will go ahead and proceed with the inspector to get the locks changed," Castle said in a voicemail to Araujo.
"I thought he was working with the bank," Araujo said. "He kept asking me when I was going to vacate."
Araujo did what she thought her bank was asking. She moved out months before her scheduled foreclosure.
"I've never done this before. I didn't know what to expect," she said.
She didn't know anything was wrong until she drove by a few weeks later and saw someone was living in her former house on Night Heron Drive just south of West Parker Road in Parker.
Kevin Potter thought he stumbled on a bargain when he found the three bedroom house on Craigslist for $600 a month.
"Everything seemed legit. He faxed me over a lease agreement and I filled it out," Potter, a single dad with four kids, said. "He gave me the code to a lock box and I looked at the house. Everything seemed legit. How would he have the key to the house?"
Potter signed a four month lease with Castle. Everything was done over e-mail. Potter says he never met Castle.
When Araujo noticed Potter and his kids had moved in, she called her bank to ask why it rented her house.
"They said, 'We don't do that. I don't know what you are talking about. You need to call your local authorities,'" Araujo said.
Parker Police told Potter he was trespassing and had to leave. Potter was forced to pull his kids out of the neighborhood school and all five of them moved into his parents' mobile home in another part of town.
"They don't have a place to call home," an emotional Potter said as he wiped tears from his eyes. "I spent over $3,000 to get into a house that obviously wasn't his."
9Wants to Know discovered Potter and Araujo aren't the only people who unknowingly got involved with Castle
On Craigslist, 9NEWS discovered Castle listed at least 21 homes from the metro area and several in Florida, Nevada, Arizona and Kansas. New homes continue to appear each month.
Homeowner after homeowner told 9NEWS Castle convinced them to sign an "Assignment of Surrender and Possession" document they thought was the final paperwork from their banks.
Some homeowners gave 9Wants to Know copies of the document. It looks official and asks questions about the condition of the home. In fine print at the bottom it says Associated Home Inspection, Castle's supposed company, has the right to take possession of the house and move new people in to "house sit" the property.
Castle collects the rent, homeowners don't get a cent. Lawyers say the document would never hold up in court as a legal contract.
"What this is, is a very clever plan to try to get people to pay him money for something he doesn't have the right to sell and that is the right to live in someone else's house," Denver attorney Andy Low said.
When viewers learned they still had the right to live in their homes, some e-mailed Castle questioning why they were asked to leave. Castle replied telling them they faced a penalty of $500,000 for any attempt to obstruct the terms of the document they signed.
9Wants to Know tried to set up a meeting with Castle to ask him about the document and the homes he offers online.
When it came time for the meeting at a Starbucks in South Denver, Castle didn't show up. A woman who claimed to work for Castle, Heidi Parks, came instead. She said she thought Castle followed the law, but admitted she's never met him.
No one 9Wants to Know spoke with during its investigation has ever met Castle.
Shortly after 9NEWS met with Parks, one of Castle's renters forwarded 9NEWS a letter from Castle with a return address for a home in Ogden, Utah.
The address traced back to Gordon Miller - a man charged in 2005 with equity skimming, mail fraud and wire fraud after prosecutors say he ran a scheme very similar to what victims claim he runs now.
When it came time for Miller to face a jury, he never showed up for court. U.S. Marshals now consider him a fugitive.
After 9Wants to Know showed United States Marshal deputies in Utah the evidence it uncovered linking Castle to Miller, deputies tell us they believe Castle and Miller are the same person.
"It appears from your investigation, and what you guys have in Colorado, that he's up to his new tricks. Same thing, just different state," Supervisor Deputy U.S. Marshal Mike Wingert said.
9Wants to Know has learned when Miller was charged in 2005, the first name of one of the attorneys involved in the case was Greg and the last name of a prosecutor was Castle.
9Wants to Know visited Miller's last known address. It's the same return address listed on letters Castle wrote to homeowners.
Miller's parents answered the door.
"He's not here," Miller's father said. "He's in Malaysia."
He told us he didn't know how to reach Miller, but another woman in the house told us she planned to visit him.
"I'm going on a cruise. I'm meeting [Gordon] on a cruise," she said as she shut the door.
The United States Marshal fugitive recovery team hasn't located Miller, but Wingert says they have new leads, though he could not discuss them. Wingert says he believes eventually Miller will be caught.
Araujo says she looks forward to the day police find Miller because she believes that will be the end of Castle too.
"I just don't see how he could take advantage of someone like that. He's obviously in it for the money," Araujo said.
To contact Jace Larson, call 303-871-1432 or e-mail email@example.com.
(Copyright KUSA*TV, All Rights Reserved)