The property listing for 11 Butler Crescent N.W. shows a "gem" of a house bookended by old trees and boasting a detached garage and handsome stucco-and-wood finish. But the photos of the little blue house in Calgary’s Brentwood neighbourhood also belie the horror that occurred there three months earlier.

Police arrested 22-year-old Matthew de Grood in connection with a stabbing spree at that address on April 15. Five students died in what was the worst mass murder in the city’s history.

The otherwise nondescript residence became a gruesome crime scene, or what the real-estate industry refers to as a "stigmatized property." While the online MLS listing makes no mention of the murders, there’s no legal obligation to do so in Alberta — or in most of Canada, for that matter.

"That’s the problem," said Mark Weisleder, a prominent Toronto property lawyer. "Everybody agrees this stigma does affect property values, and it shows that this is bothering people."

Weisleder said that most U.S. states require sellers to disclose whether a suicide or murder occurred at a property if the seller knows about such an incident within the past three years.

'The neighbours always tell'

"This whole concept of psychological stigmas is a very difficult area of the law that’s evolving in this country, but there’s no question in my mind that for [potential buyers] from certain cultures and religions, this is going to be a big issue," he said.

The Alberta Real Estate Association often reminds realtors they are under no legal requirement to release information, but there are no guarantees that prospective clients wouldn’t learn the backstory themselves, said Aruna Marathe, the organization’s associate counsel for industry relations.

Zackariah Rathwell, 21,Lawrence Hong, 27, Kaitlin Perras, 23, ​Jordan Segura, 22, and Joshua Hunter, 23, died after Matthew de Grood, 22, allegedly went on a stabbing rampage at the party in the early hours of April 15. (Facebook)

"The neighbours always tell. And in this case you have an obligation to your seller, but an ethical obligation as well," she said.

The onus is also on the buyer or the buyer’s representative to know what they don’t want.

Asking the seller the right questions then becomes paramount, said Barry Lebow, a Toronto-based forensic real estate expert and real estate broker.

In some provinces, the agent really has to become a real-estate detective. - Barry Lebow, expert witness on stigmatized properties

"In some provinces, the agent really has to become a real-estate detective," he said.

Under Ontario realtors' Code of Ethics "agents are bound to have to deal with material facts, and to deal honestly," Lebow said.

But when it comes specifically to violent crimes committed on the property, Quebec is the only jurisdiction in Canada that has disclosure laws that oblige a seller to reveal a past murder.

The trouble is realtors may not be in the know about a suicide, murder or violent crime that occurred in the home they’re asked to sell, particularly if the event did not capture widespread media attention.

Matthew de Grood, accused of stabbing five people to death at a Calgary party in April, has been charged with five counts of first-degree murder. He appeared in a Calgary court on Tuesday. (The Canadian Press)

Knowing of a murder, the seller’s representation has two options in order to comply with the "fairness, honesty and integrity" code, said Bruce Mathews, deputy registrar with the Real Estate Council of Ontario, which regulates the industry.

"They can simply say the truth — yes, a murder happened, if it’s a yes," he said. "Or if they’re under instructions from the seller not to disclose their information, they would have to say something to the effect of, ‘I’m sorry, I can’t answer that question, you’ll have to do your own research.’ And that would be a perfectly acceptable way of handling those issues."

While the real estate associate for the Brentwood house in Calgary didn’t overtly mention the stabbings, he did include an entry in a "private remarks" section viewable between realtors.

Marathe, with the Alberta Real Estate Association, said she checked the realtors-only part of the MLS listing and noticed an additional note in the section urging interested parties to call him for more information concerning the history of the property.

'Do the right thing and disclose'

"He has put in a comment to other realtors saying, basically, ‘Don’t put an offer on this property until you talk to me,’" she said. "[The seller] has obviously in this case instructed the realtor to do the right thing and disclose."

Still, it would be up to the buyer to make the inquiry in the first place.

Police found the remains or DNA of 33 women on Robert Pickton's Port Coquitlam farm. (CBC)

"If somebody chooses not to use a realtor and then becomes upset because this wasn’t disclosed, you’re not using the tools that are there effectively," Marathe said.

The key factors in the disclosure debate come down to "latent versus patent defects," explained Bill Kirk, president of the Calgary Real Estate Board.

Whereas patent defects are completely evident, such as a structural or physical problem, latent defects refer to invisible problems that may not come up during a home inspection.

"Realtors are under Canadian common law, where it’s not incumbent on a seller or an agent to divulge anything that isn’t particular to the property itself that renders the property dangerous or uninhabitable," he said. "In this particular case, it has nothing to do with the property."

A former house that operated as a marijuana grow-op might seem to be even less desirable to some clients than the house where a murder happened — if the grow-op caused mould or structural impairments, said Keith Lancastle, with the Appraisal Institute of Canada.

Bernardo home, Pickton farm demolished

"Even if two or three people were killed because of a carbon monoxide leak in the house, once that's fixed, what's going to be the impact on the property? Maybe not much," he said.

Paul Bernardo has been in maximum security prison since 1995. The former home that the notorious Ontario serial killer and rapist rented was eventually demolished. (Frank Gunn/Canadian Press)

Still, well-kept homes in prime neighbourhoods may go unsold for a prolonged time or eventually sell for below asking price owing to the "murder house" stigma.

Some properties never overcome their infamy at all.

In 2003, B.C. police ordered the demolition of buildings that once stood at serial killer Robert Pickton’s Coquitlam pig farm.

The St. Catharines, Ont., home where Paul Bernardo tortured and raped his victims was razed. The McDonald’s restaurant in Sydney River, N.S., where an employee and two of his friends shot, stabbed and beat three workers to death during a break-in was also eventually torn down.

"And the O.J. Simpson house? That was demolished, too," Lebow added.

"The Jeffrey Dahmer house, the Karla Homolka house, the Robert Pickton farm – these are not murder sites. These are notorious murder sites."

While Lebow said "natural death itself is not a big deal" when it comes to a property listing, a violent death is on "another strata."

"Read the obituaries. How often to do you see, ‘Died peacefully at home surrounded by their loved ones?’" he noted.

Marathe agreed some clients may actually take comfort in knowing a historic house was where a previous resident passed away.

"They might say, ‘Isn’t that wonderful? Somebody died happily on this property,’" she said.

Online tool for checking stigmatized properties

Aspiring homeowners curious about whether they have been eyeing stigmatized properties have a new online tool to find out.

HouseCreep.com, founded by Ottawa resident Albert Armieri and his Toronto-based brother Robert, launched last year.

"There’s a bedbugs registry, so why isn’t there a site about scenes of gruesome crimes for a prospective renter or buyer?" Armieri said. "We thought, ‘Geez, if I was buying a home and my realtor had that type of information, I would appreciate knowing.’"

The site lists more than 20,000 properties in North America. The Brentwood house has not yet been added.